Effects of Klebsiella michiganensis LDS17 on Codonopsis pilosula growth, rhizosphere soil enzyme activities, and microflora, and genome-wide analysis of plant growth-promoting genes

Codonopsis pilosula is a perennial herbaceous liana with medicinal value. It is critical to promote Codonopsis pilosula growth through effective and sustainable methods, and the use of plant growth-promoting bacteria (PGPB) is a promising candidate. In this study, we isolated a PGPB, Klebsiella michiganensis LDS17, that produced a highly active 1-aminocyclopropane-1-carboxylate deaminase from the Codonopsis pilosula rhizosphere. The strain exhibited multiple plant growth-promoting properties. The antagonistic activity of strain LDS17 against eight phytopathogenic fungi was investigated, and the results showed that strain LDS17 had obvious antagonistic effects on Rhizoctonia solani, Colletotrichum camelliae, Cytospora chrysosperma, and Phomopsis macrospore with growth inhibition rates of 54.22%, 49.41%, 48.89%, and 41.11%, respectively. Inoculation of strain LDS17 not only significantly increased the growth of Codonopsis pilosula seedlings but also increased the invertase and urease activities, the number of culturable bacteria, actinomycetes, and fungi, as well as the functional diversity of microbial communities in the rhizosphere soil of the seedlings. Heavy metal (HM) resistance tests showed that LDS17 is resistant to copper, zinc, and nickel. Whole-genome analysis of strain LDS17 revealed the genes involved in IAA production, siderophore synthesis, nitrogen fixation, P solubilization, and HM resistance. We further identified a gene (koyR) encoding a plant-responsive LuxR solo in the LDS17 genome. Klebsiella michiganensis LDS17 may therefore be useful in microbial fertilizers for Codonopsis pilosula. The identification of genes related to plant growth and HM resistance provides an important foundation for future analyses of the molecular mechanisms underlying the plant growth promotion and HM resistance of LDS17.

IMPORTANCE

We comprehensively evaluated the plant growth-promoting characteristics and heavy metal (HM) resistance ability of the LDS17 strain, as well as the effects of strain LDS17 inoculation on the Codonopsis pilosula seedling growth and the soil qualities in the Codonopsis pilosula rhizosphere. We conducted whole-genome analysis and identified lots of genes and gene clusters contributing to plant-beneficial functions and HM resistance, which is critical for further elucidating the plant growth-promoting mechanism of strain LDS17 and expanding its application in the development of plant growth-promoting agents used in the environment under HM stress.

The Multiple Promoting Effects of Suaeda glauca Root Exudates on the Growth of Alfalfa under NaCl Stress

Under abiotic stress, plant root exudates can improve plant growth performance. However, studies on the effect of root exudates on the stress resistance of another plant are insufficient. In this study, root exudates (REs) were extracted from Suaeda glauca to explore their effect on alfalfa seedlings under salt stress. The results showed that the plant height and fresh weight of alfalfa significantly increased by 47.72% and 53.39% after 7 days of RE treatment at a 0.4% NaCl concentration. Under 1.2% salt stress, REs reduced the Malondialdehyde content in alfalfa by 30.14% and increased the activity of its antioxidant enzymes (peroxidase and catalase) and the content of its osmotic regulators (soluble sugar and proline) by 60.68%, 52%, 45.67%, and 38.67%, respectively. Soil enzyme activity and the abundance of soil-beneficial bacteria were increased by REs. Spearman analysis showed that urease and neutral phosphatase were related to the richness of beneficial bacteria. Redundancy analysis confirmed that urease affected the composition of the soil bacterial community. The partial least squares structural equation model (PLS-SEM) revealed that REs had a direct positive effect on alfalfa growth under salt stress by regulating the plant's injury and antioxidant systems, and the soil bacterial community had an indirect positive effect on alfalfa growth through soil enzyme activity.

Impact of wine-grape continuous cropping on soil enzyme activity and the composition and function of the soil microbial community in arid areas

Introduction

Continuous cropping affected the stability of soil enzyme activity and the structural characteristics of microbial community. Owing to challenges in the study of complex rhizosphere microbial communities, the composition and function of these microbial communities in farmland ecosystems remain elusive. Here, we studied the microbial communities of the rhizosphere of wine grapes with different years of continuous cropping and investigated their relationships with soil enzyme activity.

Methods

Metagenomic sequencing was conducted on the rhizosphere soils from one uncultivated wasteland and four vineyards with varying durations of continuous cropping.

Results

The predominant microbial were bacteria (98.39%), followed by archaea (1.15%) and eukaryotes (0.45%). Continuous cropping caused a significant increase in the relative abundance of Rhizobiales and Micrococcales but a marked decrease in Solirubrobacterales. At the genus level, 75, 88, 65, 132, and 128 microbial genera were unique to uncultivated wasteland, 5, 10, 15, and 20 years of continuous cropping, respectively. The relative abundance of genes with signal transduction function was the highest. The activity of all enzymes measured in this study peaked at 5 years of continuous cropping, and then decreased with 10 to 15 year of continuous cropping, but increased at 20 years again. In addition, soil enzyme activity, especially of alkaline phosphatase was significantly correlated with the diversity of the dominant microorganisms at the genus level. Moreover, the coupled enzyme activities had a greater impact on the diversity of the microbial community than that of individual enzymes.

Conclusion

Our findings reveal the composition and function of the soil microbial communities and enzymes activity in response to changes in cropping years, which has important implications for overcoming continuous cropping obstacles and optimizing land use.

Role of Soil Microbiota Enzymes in Soil Health and Activity Changes Depending on Climate Change and the Type of Soil Ecosystem

The extracellular enzymes secreted by soil microorganisms play a pivotal role in the decomposition of organic matter and the global cycles of carbon (C), phosphorus (P), and nitrogen (N), also serving as indicators of soil health and fertility. Current research is extensively analyzing these microbial populations and enzyme activities in diverse soil ecosystems and climatic regions, such as forests, grasslands, tropics, arctic regions and deserts. Climate change, global warming, and intensive agriculture are altering soil enzyme activities. Yet, few reviews have thoroughly explored the key enzymes required for soil fertility and the effects of abiotic factors on their functionality. A comprehensive review is thus essential to better understand the role of soil microbial enzymes in C, P, and N cycles, and their response to climate changes, soil ecosystems, organic farming, and fertilization. Studies indicate that the soil temperature, moisture, water content, pH, substrate availability, and average annual temperature and precipitation significantly impact enzyme activities. Additionally, climate change has shown ambiguous effects on these activities, causing both reductions and enhancements in enzyme catalytic functions.

Colonization and phytoremediation potential for Miscanthus sacchariflorus in copper tailings

A pot experiment was conducted to explore the effects of copper (Cu) tailings with various proportions in the substrate on seed germination and morphological traits of the plant. Concurrently, to identify the adaptive and tolerance strategies of the plant to Cu tailings, the uptake and accumulation of the plant to heavy metals, variations in soil enzymatic activities, and metal speciation in the blank, rhizospheric, and non-rhizospheric soils were estimated. Cu tailings at 25% proportion in the substrate exerted no significant negative effects on seed germination and seedling growth. However, Cu tailings at higher proportions (≧50%) inhibited seed germination and disturbed the plant physiological metabolism and growth. More biomass allocated to the plant roots could contribute to more heavy metals being immobilized, arresting their translocation from roots to shoots. This was accepted as a crucial defense mechanism for the plant against heavy metal co-contamination. The plant can improve the biological properties of Cu tailings in terms of enhanced invertase and phosphatase activities. And in turn, this can effectively alleviate heavy metal phytotoxicity. Simultaneously, it markedly decreased exchangeable Cu and Zn content in the rhizosphere in 25% Cu tailings treatments. In 50% Cu tailings treatment, no differences were observed in Zn speciation between rhizosphere and non-rhizosphere soils. In 75% Cu tailings, compared to the non-rhizosphere, an obvious reduction in exchangeable Cu in rhizosphere occurred, while an opposite tendency was demonstrated in carbonate-bound Zn. The plant could successfully colonize in Cu tailings, and represent a phytoremediation potential in Cu tailings.

The impact of smash-ridge tillage on agronomic traits of tobacco plants, soil enzymatic activity, microbial community structure, and functional diversity

Smash-ridge tillage is a novel cultivation technique that significantly influences the quality of arable land and crop yield. In this study, we employed high-throughput 16S rRNA sequencing and Biolog-ECO methods to systematically investigate the impact of smash-ridge tillage on soil microbial community structure and functional diversity. The results demonstrate that both ST30 and ST50 treatments significantly enhance the average plant height, average plant diameter, average fresh root weight, stem fresh weight, and leaf area of tobacco plants, with the ST50 treatment exhibiting superior performance. Furthermore, both ST30 and ST50 treatments exhibit significantly higher soil enzyme activity and microbial community diversity compared to the CK treatment. They also improve the soil microbial utilization of carbon sources. Additionally, the ST50-treated soil samples demonstrate 15 microbial functional pathways that exceed those of the CK and ST30 treatments. In conclusion, the Smash-ridge tillage treatment at a depth of 50 cm yields more favorable results. This study provides a theoretical foundation for enhancing soil quality in Smash-ridge tillage by elucidating the mechanisms through which it impacts soil microbial ecology.

Responses of the maize rhizosphere soil environment to drought-flood abrupt alternation stress

Changes in the soil environment in the root zone will affect the growth, development and resistance of plants. The mechanism underlying the effect of drought and flood stress on rhizosphere bacterial diversity, soil metabolites and soil enzyme activity is not clear and needs further study. To analyze the dynamic changes in bacteria, metabolites and enzyme activities in the rhizosphere soil of maize under different drought-flood abrupt alternation (DFAA) stresses, the barrel test method was used to set up the 'sporadic light rain' to flooding (referring to trace rainfall to heavy rain) (DFAA1) group, 'continuous drought' to flooding (DFAA2) group and normal irrigation (CK) group from the jointing to the tassel flowering stage of maize. The results showed that Actinobacteria was the most dominant phylum in the two DFAA groups during the drought period and the rewatering period, and Proteobacteria was the most dominant phylum during the flooding period and the harvest period. The alpha diversity index of rhizosphere bacteria in the DFAA2 group during the flooding period was significantly lower than that in other stages, and the relative abundance of Chloroflexi was higher. The correlation analysis between the differential genera and soil metabolites of the two DFAA groups showed that the relative abundance of Paenibacillus in the DFAA1 group was higher during the drought period, and it was significantly positively correlated with the bioactive lipid metabolites. The differential SJA-15 bacterium was enriched in the DFAA2 group during the flooding period and were strongly correlated with biogenic amine metabolites. The relative abundances of Arthrobacter, Alphaproteobacteria and Brevibacillus in the DFAA2 group were higher compared with DFAA1 group from rewatering to harvest and were significantly positively correlated with hydrocarbon compounds and steroid hormone metabolites. The acid phosphatase activity of the DFAA1 group was significantly higher than that of the DFAA2 group during the flooding period. The study suggests that there is a yield compensation phenomenon in the conversion of 'continuous drought' to flooding compared with 'sporadic light rain', which is related to the improvement in the flooding tolerance of maize by the dominant bacteria Chloroflexi, bacterium SJA-15 and biogenic amine metabolites. These rhizosphere bacteria and soil metabolites may have the potential function of helping plants adapt to the DFAA environment. The study revealed the response of the maize rhizosphere soil environment to DFAA stress and provided new ideas for exploring the potential mechanism of crop yield compensation under DFAA.

Controlled-Release Nitrogen Mixed with Common Nitrogen Fertilizer Can Maintain High Yield of Rapeseed and Improve Nitrogen Utilization Efficiency

Field experiments were conducted to study the effects of different proportions of controlled-release nitrogen fertilizer mixed with quick-acting nitrogen fertilizer on the yield and nitrogen utilization efficiency of direct-seeding rapeseed. Using a conventional nitrogen application rate of 180 kg ha-1 as a control, a total of 5 types of available nitrogen fertilizers and different proportions of controlled-release nitrogen fertilizers were mixed for fertilizer treatment. The proportion of available nitrogen fertilizer used was 135 kg ha-1, and the addition ratios of the five types of controlled-release nitrogen fertilizers were 0%, 30%, 50%, 70%, and 100%, respectively (i.e., the proportion of controlled-release nitrogen to the total nitrogen application amount). These ratios were represented as N135R0, N135R1, N135R2, N135R3, and N135R4, respectively. The results showed that there was no significant difference in the number of pods per plant, the number of seeds per pod, or the grain yield under the treatment of controlled-release nitrogen fertilizer mixed with quick-acting nitrogen fertilizer for proportions of 30-50% (N135R1~R3) when compared with the control, and a stable yield was achieved. Mixing controlled-release nitrogen fertilizer under reduced nitrogen application can significantly improve the apparent utilization rate of rapeseed nitrogen fertilizer, but it first increases and then decreases with the increase of the controlled-release nitrogen mixing ratio, reaching its highest under the N135R2 treatment. The agronomic utilization efficiency and partial productivity of nitrogen fertilizer first increased and then decreased with the increased proportion of controlled-release nitrogen, and both reached their highest utilization with the N135R2 treatment. The mixed treatment of controlled-release nitrogen did not affect soil urease activity, but significantly increased soil sucrase activity. The mixed treatment of controlled-release nitrogen also increased soil microbial biomass nitrogen and carbon content. Especially in the flowering stage, the soil microbial biomass nitrogen and carbon content was significantly higher under a controlled-release nitrogen mixing ratio of 30-50%. At the same time, it had a similar effect on soil inorganic nitrogen content. Therefore, a controlled-release nitrogen mixing treatment provided sufficient nitrogen for the key growth period of rapeseed. Under the condition of reducing the amount of nitrogen fertilizer by 25% based on the amount of nitrogen fertilizer applied to conventional rapeseed, the application of controlled-release urea mixed with common nitrogen fertilizer mixed at a ratio of 30-50% can be an effective way to maintain grain yield levels and improve nitrogen utilization efficiency.

[Ecological Responses of Soil Bacterial Communities to Heavy Metal Contamination Surrounding a Typical Coal-based Industrial Region]

Microbial communities in the soil might be affected by heavy metal contamination caused by anthropogenic activities associated with the coal-based industry. This study analyzed the differences in soil physicochemical properties, heavy metal concentrations, and enzyme activities surrounding different coal-based industrial fields(coal mining industry, coal preparation industry, coal-based chemical industry, and coal-fired power industry) in Shanxi Province, North China. Moreover, soil samples from farmland and parks away from all the industrial plants were collected as references. Based on the 16S rRNA high-throughput sequencing, we identified the composition of soil bacterial communities. Spearman correlation and redundancy analyses were used to explore the relationships between soil bacterial communities and environmental factors. The results showed that the concentrations of most heavy metals were greater than the local background values, particularly for As, Pb, and Cd, but they did not exceed the risk screening values of Soil Environment Quality:Risk Control Standard for Soil Contamination of Agriculture Land(GB 15618-2018). There were significant differences in soil cellulase and alkaline phosphatase activities among sampling fields. Actinobacteria was the predominant bacterial phyla, with the highest relative abundance surrounding the coal-based chemical plants, followed by Proteobacteria. The soil bacterial communities were significantly affected by Cd, total carbon, total nitrogen, and alkaline phosphatase activity. This study could provide a foundation for the ecological remediation of the coal-based industrial region in the future.

Mechanism of Salt Tolerance and Plant Growth Promotion in Priestia megaterium ZS-3 Revealed by Cellular Metabolism and Whole-Genome Studies

Approximately one-third of agricultural land worldwide is affected by salinity, which limits the productivity and sustainability of crop ecosystems. Plant-growth-promoting rhizobacteria (PGPR) are a potential solution to this problem, as PGPR increases crop yield through improving soil fertility and stress resistance. Previous studies have shown that Priestia megaterium ZS-3(ZS-3) can effectively help plants tolerate salinity stress. However, how ZS-3 regulates its metabolic adaptations in saline environments remains unclear. In this study, we monitored the metabolic rearrangement of compatibilisers in ZS-3 and combined the findings with genomic data to reveal how ZS-3 survives in stressful environments, induces plant growth, and tolerates stress. The results showed that ZS-3 tolerated salinity levels up to 9%. In addition, glutamate and trehalose help ZS-3 adapt to osmotic stress under low NaCl stress, whereas proline, K+, and extracellular polysaccharides regulate the osmotic responses of ZS-3 exposed to high salt stress. Potting experiments showed that applying the ZS-3 strain in saline and neutral soils could effectively increase the activities of soil acid phosphatase, urease, and invertase in both soils, thus improving soil fertility and promoting plant growth. In addition, strain ZS-3-GFP colonised the rhizosphere and leaves of Cinnamomum camphora well, as confirmed by confocal microscopy and resistance plate count analysis. Genomic studies and in vitro experiments have shown that ZS-3 exhibits a variety of beneficial traits, including plant-promoting, antagonistic, and other related traits (such as resistance to saline and heavy metal stress/tolerance, amino acid synthesis and transport, volatile compound synthesis, micronutrient utilisation, and phytohormone biosynthesis/regulatory potential). The results support that ZS-3 can induce plant tolerance to abiotic stresses. These data provide important clues to further reveal the interactions between plants and microbiomes, as well as the mechanisms by which micro-organisms control plant health.

The impact of main Areca Catechu root exudates on soil microbial community structure and function in coffee plantation soils

Coffee is an important cash crop worldwide, but it has been plagued by serious continuous planting obstacles. Intercropping with Areca catechu could alleviate the continuous planting obstacle of coffee due to the diverse root secretions of Areca catechu. However, the mechanism of Areca catechu root secretion in alleviating coffee continuous planting obstacle is still unclear. The changes of coffee rhizosphere soil microbial compositions and functions were explored by adding simulated root secretions of Areca catechu, the primary intercropping plant species (i.e., amino acids, plant hormone, organic acids, phenolic acids, flavonoids and sugars) in current study. The results showed that the addition of coffee root exudates altered soil physicochemical properties, with significantly increasing the availability of potassium and organic matter contents as well as promoting soil enzyme activity. However, the addition of plant hormone, organic acids, or phenolic acids led to a decrease in the Shannon index of bacterial communities in continuously planted coffee rhizosphere soil (RS-CP). The inclusion of phenolic acids specifically caused the decrease of fungal Shannon index. Plant hormone, flavonoids, phenolic acids, and sugars increased the relative abundance of beneficial bacteria with reduced bacterial pathogens. Flavonoids and organic acids increased the relative abundance of potential fungal pathogen Fusarium. The polyphenol oxidase, dehydrogenase, urease, catalase, and pH were highly linked with bacterial community structure. Moreover, catalase, pH, and soil-available potassium were the main determinants of fungal communities. In conclusion, this study highlight that the addition of plant hormone, phenolic acids, and sugars could enhance enzyme activity, and promote synergistic interactions among microorganisms by enhancing the physicochemical properties of RS-CP, maintaining the soil functions in coffee continuous planting soil, which contribute to alleviate the obstacles associated with continuous coffee cultivation.

Legume-grass mixtures increase forage yield by improving soil quality in different ecological regions of the Qinghai-Tibet Plateau

Introduction

Information on the relationship between soil quality and forage yield of legume-grass mixtures in different ecological regions can guide decision-making to achieve eco-friendly and sustainable pasture production. This study's objective was to assess the effects of different cropping systems on soil physical properties, nitrogen fractions, enzyme activities, and forage yield and determine suitable legume-grass mixtures for different ecoregions.

Methods

Oats (Avena sativa L.), forage peas (Pisum sativum L.), common vetch (Vicia sativa L.), and fava beans (Vicia faba L.) were grown in monocultures and mixtures (YS: oats and forage peas; YJ: oats and common vetch; YC: oats and fava beans) in three ecological regions (HZ: Huangshui Valley; GN: Sanjiangyuan District; MY: Qilian Mountains Basin) in a split-plot design.

Results

The results showed that the forage yield decreased with increasing altitude, with an order of GN (3203 m a.s.l.; YH 8.89 t·ha-1) < HZ (2661 m; YH 9.38 t·ha-1) < MY (2513m; YH 9.78 t·ha-1). Meanwhile, the forage yield was higher for mixed crops than for single crops in all ecological regions. In the 0-10 cm soil layer, the contents of total nitrogen (TN), microbial biomass nitrogen (MBN), soil organic matter (SOM), soluble organic nitrogen (SON), urease (UE), nitrate reductase (NR), sucrase (SC), and bacterial community alpha diversity, as well as relative abundance of dominant bacteria, were higher for mixed crops than for oats unicast. In addition, soil physical properties, nitrogen fractions, and enzyme activities varied in a wider range in the 0-10 cm soil layer than in the 10-20 cm layer, with larger values in the surface layer than in the subsurface layer. MBN, SON, UE, SC and catalase (CAT) were significantly and positively correlated with forage yield (P < 0.05). Ammonium nitrogen (ANN), nitrate nitrogen (NN), SOM and cropping systems (R) were significantly and positively correlated with Shannon and bacterial community (P < 0.05). The highest yields in the three ecological regions were 13.00 t·ha-1 for YS in MY, 10.59 t·ha-1 for YC in GN, and 10.63 t·ha-1 for YS in HZ.

Discussion

We recommend planting oats and forage peas in the Qilian Mountains Basin, oats and fava beans in the Sanjiangyuan District, and oats and forage peas in Huangshui valley. Our results provide new insights into eco-friendly, sustainable, and cost-effective forage production in the Qinghai Alpine Region in China.

[Effects of Supplementation of Different Amendments on Soil Heavy Metals and Enzyme Activities in Coastal Saline Land]

The supplementation of soil amendments may not only improve the soil physical and chemical properties but also lead to the accumulation of heavy metals in soil. This experiment included six treatments:control (CK), organic manure (OM), polyacrylamide+organic manure (PAM+OM), straw mulching+organic manure (SM+OM), buried straw+organic manure (BS+OM), and bio-organic manure+organic manure (BM+OM) to explore the effects of different soil amendments on heavy metals and soil enzyme activities in coastal saline land and the relationship between them. The results revealed that compared with that in the CK treatment, the contents of soil Cr, Cu, Ni, and Pb exhibited an upward trend after the supplementation of soil amendments, among which the SM+OM and PAM+OM treatments had the most significant effects on the contents of soil Cr and Cu, respectively, whereas the BM+OM treatment had the most significant effects on the contents of soil Ni and Pb. Compared with those in the CK treatment, the activities of soil invertase and urease increased significantly following supplementation of soil amendments, and the BM+OM treatment had the best effect. The alkaline phosphatase activity exhibited a slightly upward trend after the supplementation of soil amendments, whereas the catalase activity did not change significantly. The redundancy analysis revealed that the first two axes cumulatively accounted for 70.3% of the variability in enzyme activities, and the importance of single soil heavy metals on soil enzyme activity was as follows:Ni>Cu>Cr>Pb.

Arbuscular Mycorrhizal Fungi Restored the Saline-Alkali Soil and Promoted the Growth of Peanut Roots

Peanut (Arachis hypogaea L.) is an important oil and cash crop. An efficient utilization of saline-alkali soil resources, the development of peanut planting in saline-alkali soil, and obtaining high and stable yield have become urgent needs to ensure peanut production. Arbuscular mycorrhizal fungi (AMF) have been reported to develop the potential productivity of host plants and improve their salt resistance and tolerance. However, there is still limited research on promoting the growth and morphology of peanut roots. Therefore, in this study, seeds of salt-tolerant peanut variety "HY 25" were coated with commercial AMF inoculant before being planted in saline-alkali and normal soils to investigate the effects of AMF on peanut root growth and rhizosphere soil. The results showed that root morphological characteristics were significantly increased by the use of AMF at the podding stage in saline-alkali soil and from the flowering and pegging stage to the maturity stage in normal soil. Of note, the total root volume of peanut inoculated with AMF significantly increased by 31.57% during the podding stage in saline-alkali soil. Meanwhile, AMF significantly increased the phosphatase and invertase activities in the peanut rhizosphere of saline-alkali soil from the flowering stage to maturity stage and soil CAT activity at the maturity stage (41.16~48.82%). In normal soil, soil phosphatase and urease activities were enhanced by AMF at the flowering stage and the podding stage, respectively. AMF also increased the contents of soil organic matter, available phosphorus, and hydrolysable nitrogen, but decreased soil EC in saline-alkali soil. In addition to the significant increase in soil available phosphorus content, AMF had no significant effect on the physical and chemical properties of the soil and other soil nutrients in normal soil. AMF significantly increased pod biomass and yield in saline-alkali soil and normal soil, and improved their agronomic characteristics. In conclusion, peanut seeds coated with AMF improved the root morphological characteristics of peanuts and improved the physical and chemical properties in peanut rhizosphere, especially in saline-alkali soil. The process of rhizosphere soil nutrient transformation was also enhanced. Finally, AMF improved plant agronomic traits to increase the pod yield (16.5~21.9%). This study provides the theoretical basis and technical support for the application of AMF in peanut production in saline-alkali soil.

Effects of partial substitution of chemical fertilizer with organic manure on the activity of enzyme and soil bacterial communities in the mountain red soil

Introduction

The partial substitution of chemical fertilizer with organic manure takes on a critical significance to enhancing soil quality and boosting sustainable agricultural development. However, rare research has studied the effects of partial substitution of chemical fertilizer with organic manure on soil bacterial community diversity and enzyme activity in maize field in the mountain red soil region of Yunnan.

Methods

In this study, four treatments were set up in which chemical fertilizer (the application rates of N, P2O5 and K2O were 240, 75 and 75 kg·ha-1, respectively) was substituted by 10% (M10), 20% (M20), 30% (M30) and 40% (M40) of organic manure with equal nitrogen, as well as two control treatments of single application of chemical fertilizer (M0) and no fertilization (CK). The maize (Zea mays L.) crop was sown as a test crop in May 2018. The effects of partial substitution of chemical fertilizer with organic manure on soil physicochemical properties, soil bacterial community diversity and enzyme activity were studied.

Results

The activities of Cellulase (CBH), Invertase (INV) and β-glucosidase (BG) increased with the increase of organic manure substitution ratio. The activities of β-1,4-N-acetylglucosaminidase (NAG), Urease (URE), and leucine aminopeptidase (LAP) also had the same trend, but the highest activities were 159.92 mg·g-1·h-1, 66.82 mg·g-1·h-1 and 143.90 mg·g-1·h-1 at 30% substitution ratio. Compared with CK and M0 treatments, Shannon index increased notably by 82.91%-116.74% and 92.42%-128.01%, respectively, at the organic manure substitution ratio ranging from 10% to 40%. Chao1 and ACE index increased significantly at the organic manure substitution ratio ranging from 10% to 30%. Proteobacteria was the dominant phylum in all treatments, the relative abundance of Proteobacteria decreased as the organic manure substitution ratio increased. Redundancy analysis showed that microbial biomass C was the main factor affecting the bacterial community composition under partial replacement of chemical fertilizer treatment, while Actinobacteria was the main factor affecting the enzyme activity. In addition, the maize yield of M30 and M40 treatments was significantly higher than that of CK and M0-M20 treatments, and the yield of M30 treatment was the highest, reaching 7652.89 kg·ha-1.

Conclusion

Therefore, the partial substitution of chemical fertilizer with organic manure can improve soil biological characteristics, while increasing bacterial community diversity and soil enzyme activity. Therefore, a thirty percent organic manure substitution was determined as the optimal substitution ratio for maize farmland in the mountain red soil area of Yunnan, China.

Effects of drip irrigation on yield, soil fertility and soil enzyme activity of different potato varieties in Northwest China

The effects of different irrigation and fertilization on potato yield, soil fertility and soil enzyme activity of different varieties under drip irrigation fertilization mode were studied, which could provide support for selecting the best varieties in Northwest China. Three factors and three levels orthogonal experimental design method, a total of nine treatments. The three irrigation levels were W1 (100% crop evapotranspiration (ETC)), W2 (80% ETC) and W3 (60% ETC). The three fertilization levels were F1 (N-P2O5-K2O, 240-120-300 kg ha-1), F2 (180-90-225 kg ha-1) and F3 (120-60-150 kg ha-1). The three varieties were V1 (Feiuritar), V2 (Longshu7) and V3 (Qingshu 9). The results showed that different irrigation and fertilization had significant effects on potato yield, soil fertility and soil enzyme activity in root zone. The highest yield of T5 (80%ETC, 180-90-225 kg ha-1, Qingshu 9) was 49,222.3 kg ha-1. With the increase of fertilizer application rate, potato yield and soil enzyme activity in root zone increased first and then decreased, but soil electrical conductivity (SEC), soil nitrate-N content (SNNC), soil alkali-hydrolyzable nitrogen content (SAHC), soil available potassium (AK), soil available phosphorus (AP), soil ammonium-N content (SANC) and soil organic matter (SOM) in root zone increased continuously. The yield, soil catalase activity, soil urease activity and soil sucrase activity at W2 were 2.81% and 22.2%, 1.84% and 7.04%, 8.26% and 9.62%, 5.34% and 13.36% higher than those at W1 and W3, respectively. The overall trend of soil water content, soil nutrient content and enzyme activity in root zone was 0-20 cm >20-40 cm >40-60 cm soil layer. There were many soil factors affecting tuber yield, among which soil enzyme activity, pH value and root zone conductivity were the key factors. The results showed that T5 (80%ETC, 180-90-225 kg ha-1, Qingshu 9) was the best treatment to improve soil enzyme activity and yield.

Effects of Straw Mulching on Soil Properties and Enzyme Activities of Camellia oleifera-Cassia Intercropping Agroforestry Systems

In order to explore the influences of rice straw mulching on soil fertility in agroforestry systems, the soil C and N contents and enzyme activities were investigated in a C. oleifera-cassia intercropping ecosystem in Central Southern China. Three straw mulching application treatments were set up in this study, in 2021, namely, straw powder mulching (SPM), straw segment mulching (SSM), and non-straw mulching as the control (CK). Soil samples were collected from three soil depths (0-10 cm,10-20 cm, and 20-40 cm) in each treatment on the 90th-day after the treatments. The soil organic carbon (SOC), total nitrogen (TN), microbial carbon (MBC), soil enzyme activities (including acid phosphatase (ACP), urease (UE), cellulase (CL), and peroxidase (POD)), and soil water content (SWC) were determined. The results showed that the SOC significantly increased due to the mulching application in SPM and SSM, in the topsoil of 0-10 cm when compared to the CK. The SWC, SOC, TN, and MBC increased by 0.8 and 56.5, 3.5 and 37.5, 21.3 and 61.6, and 5.8% and 76.8% in the SPM and SSM treatments compared to the CK, respectively. The soil enzyme activities of ACP, UE, CE, and POD increased significantly due to straw mulching compared with CK throughout all soil layers. The soil enzyme activities of CL and POD were significantly higher in SSM than in SPM across the soil depth except for ACP. The enzyme activities of ACP were 14,190, 12,732, and 6490 U/g in SSM, SPM, and control, respectively. This indicated that mulching application enhanced the enzyme activity of ACP. Mulching had no significant effects on UE and CL, while the POD decreased significantly in the order of SPM > SSM > CK across all soil layers, being, on average, 6.64% and 3.14% higher in SSM and SPM, respectively, compared to the CK plots. The SOC and MBC were the key nutrient factors affecting the soil enzyme activities at the study site. The results from this study provided Important scientific insights for improving soil physicochemical properties during the management of the C. oleifera intercropping system and for the development of the C. oleifera industry.

Enzyme activities and heavy metal interactions in calcareous soils under different land uses

This study was carried out to examine the interaction of enzyme activities, microbial biomass carbon, and CO2 respiration with heavy metals under different land uses in terms of quality and sustainability of the soil. There is a statistically significant positive correlation between dehydrogenase enzyme activity and Mn, Pb, Cd, and Co, while it was negative between Cr. There was a positive correlation between catalase enzyme activity and Mn and Pb and between urease and Co. The higher interaction of dehydrogenase activity with heavy metals, which is included in the endo enzyme group, has been explained as a much stronger effect of heavy metals on living microorganisms and endoenzymes than extracellular enzymes stabilized on clay minerals and organic matter. The high clay content of the soil is thought to reduce some of the negative effects of heavy metals on enzymes. The results of this study may be good indicators of enzyme activities, especially dehydrogenase, catalase, and urease, for soil health and quality, chemical degradation and restoration processes, and ecosystem functioning in soils contaminated or to be contaminated with heavy metals. It shows that the activities of these enzymes are very sensitive and can decrease rapidly in case of high concentrations of heavy metals.

Short-term legacy effects of long-term nitrogen and water addition on soil chemical properties and micro-bial characteristics in a temperate grassland

Nitrogen deposition and summer precipitation in eastern Inner Mongolia are predicted to increase in recent decades. However, such increases in nitrogen inputs and precipitation may not be continuous under the future new patterns of global change, with the direction and magnitude of which may change or weaken. The legacy effects of nitrogen and water addition after cessation on ecosystems are still unclear. Based on a 13-year nitrogen and water addition experiment in temperate grassland of northern China, we examined the short-term (2 years) legacy effects of historical nitrogen and water addition on soil physicochemical properties and microbial properties after the cessation of nitrogen and water addition in the 14th year. The results showed that the positive effects of historical nitrogen addition on most of soil nutrient variables diminished after two years of cessation, including ammonium nitrogen, nitrate nitrogen, dissolved organic carbon and nitrogen, and Olsen-P concentrations. In contrast, there were legacy effects on soil microbial characteristics. For example, the historical nitrogen input of 15 g N·m-2·a-1 reduced microbial biomass carbon, respiration, and alkaline phosphomonoesterase activity by 73.3%, 81.9%, and 70.3% respectively. It implied that microbial parameters restored slowly in comparison with soil nutrients, showing a hysteresis effect. Results of Pearson's correlation and redundancy analysis showed that the legacy effects of historical nitrogen addition on microbial parameters could be attributed to the negative effects of nitrogen addition on soil pH. Historical water addition showed significant legacy effects on soil pH, ammonium nitrogen, dissolved organic carbon and nitrogen, respiration, and soil enzyme activities, which significantly interacted with historical nitrogen addition. These results are of great significance to predict the changes in grassland ecosystem functions and services under the local environmental improvement conditions, and to reveal the restoration mechanism of degraded grassland.

Contrasting effects of organic materials versus their derived biochars on maize growth, soil properties and bacterial community in two type soils

The objective of this study was to assess the benefit of applying biochar instead of its feedstock in enhancing soil quality. To accomplish this, we investigated the short-term effects of two organic materials and their derived biochars on maize growth, soil properties, and microbial community in fluvo-aquic and red soil with a pot experiment. Five treatments were applied to each soil, namely, the addition of straw, manure, straw-derived biochar, manure-derived biochar, and the control with no addition of any organic materials and biochar. Our results revealed that straw decreased the shoot biomass of maize in both soils, while straw-derived biochar, manure and manure-derived biochar increased it by 51.50, 35.47 and 74.95% in fluvo-aquic soil and by 36.38, 117.57 and 67.05% in red soil compared with the control, respectively. Regarding soil properties, although all treatments increased soil total organic carbon, straw and manure exhibited more pronounced effects on improving permanganate-oxidizable carbon, basal respiration, and enzyme activity compared with their derived biochars. Manure and its biochar had more significant effects on improving soil available phosphorus, whereas straw and its biochar exhibited more ameliorating effects on available potassium. Straw and manure consistently decreased bacterial alpha diversity (Chao1 and Shannon index) and altered bacterial community composition in the two soils by increasing the relative abundances of Proteobacteria, Firmicutes, and Bacteroidota and decreasing those of Actinobacteriota, Chloroflexi, and Acidobacteriota. More specifically, straw had a greater effect on Proteobacteria, whereas manure affected Firmicutes more. While straw-derived biochar had no effect on bacterial diversity and bacterial community composition in both soils, manure-derived biochar increased bacterial diversity in the fluvo-aquic soil and altered bacterial community composition in the red soil by increasing the relative abundances of Proteobacteria and Bacteroidota and decreasing that of Firmicutes. In summary, owing to the input of active organic carbon, straw and manure exhibited more pronounced short-term effects on soil enzyme activity and bacterial community compared with their derived biochar. Furthermore, straw-derived biochar was found to be a better option than straw in promoting maize growth and nutrient resorption, while the choice of manure and its biochar should be determined by the soil type.

Ecological Responses of Soil Microbial Communities to Heavy Metal Stress in a Coal-Based Industrial Region in China

Soil microorganisms play vital roles in ecosystem functions, and soil microbial communities might be affected by heavy metal contamination caused by the anthropogenic activities associated with the coal-based industry. This study explored the effects of heavy metal contamination on soil bacterial and fungal communities surrounding different coal-based industrial fields (the coal mining industry, coal preparation industry, coal-based chemical industry, and coal-fired power industry) in Shanxi province, North China. Moreover, soil samples from farmland and parks away from all the industrial plants were collected as references. The results showed that the concentrations of most heavy metals were greater than the local background values, particularly for arsenic (As), lead (Pb), cadmium (Cd), and mercury (Hg). There were significant differences in soil cellulase and alkaline phosphatase activities among sampling fields. The composition, diversity, and abundance of soil microbial communities among all sampling fields were significantly different, particularly for the fungal community. Actinobacteria, Proteobacteria, Chloroflexi, and Acidobacteria were the predominant bacterial phyla, while Ascomycota, Mortierellomycota, and Basidiomycota dominated the studied fungal community in this coal-based industrially intensive region. A redundancy analysis, variance partitioning analysis, and Spearman correlation analysis revealed that the soil microbial community structure was significantly affected by Cd, total carbon, total nitrogen, and alkaline phosphatase activity. This study profiles the basic features of the soil physicochemical properties, the multiple heavy metal concentrations, and the microbial communities in a coal-based industrial region in North China.

Soil chemistry, metabarcoding, and metabolome analyses reveal that a sugarcane-Dictyophora indusiata intercropping system can enhance soil health by reducing soil nitrogen loss

Introduction

Greater amounts of fertilizer are applied every year to meet the growing demand for food. Sugarcane is one of the important food sources for human beings.

Methods

Here, we evaluated the effects of a sugarcane-Dictyophora indusiata (DI) intercropping system on soil health by conducting an experiment with three different treatments: (1) bagasse application (BAS process), (2) bagasse + DI (DIS process), and (3) the control (CK). We then analyzed soil chemistry, the diversity of soil bacteria and fungi, and the composition of metabolites to clarify the mechanism underlying the effects of this intercropping system on soil properties.

Results and discussion

Soil chemistry analyses revealed that the content of several soil nutrients such as nitrogen (N) and phosphorus (P) was higher in the BAS process than in the CK. In the DIS process, a large amount of soil P was consumed by DI. At the same time, the urease activity was inhibited, thus slowing down the loss of soil in the DI process, while the activity of other enzymes such as β-glucosidase and laccase was increased. It was also noticed that the content of lanthanum and calcium was higher in the BAS process than in the other treatments, and DI did not significantly alter the concentrations of these soil metal ions. Bacterial diversity was higher in the BAS process than in the other treatments, and fungal diversity was lower in the DIS process than in the other treatments. The soil metabolome analysis revealed that the abundance of carbohydrate metabolites was significantly lower in the BAS process than in the CK and the DIS process. The abundance of D(+)-talose was correlated with the content of soil nutrients. Path analysis revealed that the content of soil nutrients in the DIS process was mainly affected by fungi, bacteria, the soil metabolome, and soil enzyme activity. Our findings indicate that the sugarcane-DIS intercropping system can enhance soil health.

Responses of soil enzyme activity to freeze-thaw alternation in Greater Khingan Mountains, China

We examined the effects of freeze-thaw cycles (0, 1, 3, 5, 7, 15 cycles) on the activities of urease, invertase, and proteinase in the different layers of the soil under the four typical stands in the cold temperate zone, i.e., Pinus pumila stand, Rhododendron-Betula platyphylla stand, Rhododendron-Larix gmelinii stand, Ledum-Larix gmelinii stand, with the indoor freeze-thaw simulation culture method being used. The relationship between soil enzyme activity and multiple physicochemical variables was analyzed during freeze-thaw alternation. The results showed that the activity of soil urease was firstly increased and then inhibited during freeze-thaw alternation. After freeze-thaw, urease activity did not differ from that without freeze-thaw. Invertase activity was firstly inhibited and then increased during freeze-thaw alternation, and was significantly increased by 8.5%-40.3% after freeze-thaw. Proteinase activity was firstly increased and then inhibited during freeze-thaw alternation, and was significantly decreased by 13.8%-68.9% after freeze-thaw. After freezing and thawing, there was significant positive correlation between urease activity and ammonium nitrogen and soil water content in Ledum-L. gmelinii stand and P. pumila stand, respectively, and proteinase activity had significant negative correlation with inorganic nitrogen concentration in P. pumila stand, Rhododendron-B. platyphylla stand, and Ledum-L. gmelinii stand. Invertase activity had significant positive correlation with organic matter in Rhododendron-L. gmelinii stand and Ledum-L. gmelinii stand.

Effects of different concentrations of biochar amendments and Pb toxicity on rhizosphere soil characteristics and bacterial community of red clover (Trifolium pretense L.)

Amending soil with biochar can reduce the toxic effects of heavy metals (HM) on plants and the soil. However, the effects of different concentrations of biochar on the properties and microbial activities in lead (Pb)-contaminated soils are unclear. In this study, two Pb concentrations were set (low, 1000 mg/kg; high, 5000 mg/kg), and five corn straw biochar (CSB) concentrations (0, 2.5, 5, 10 and 15%) were used to determine the response of the growth and rhizosphere of red clover (Trifolium pretense L.) (in terms of soil properties and bacteria) to CSB and Pb application. The results showed that 5% CSB better alleviated the toxicity of Pb on the shoot length of red clover, the biomass increased by 74.55 and 197.76% respectively and reduced the enrichment factor (BCF) and transport factor (TF) of red clover. Pb toxicity reduced soil nutrients, catalase (CAT), acid phosphatase (ACP) and urease activity, while the addition of CSB increased soil pH, soil organic matter (SOM) content and soil enzyme activity. 16S rDNA amplicon sequencing analysis showed that Pb toxicity reduced the diversity of rhizosphere bacteria in red clover and reduced the relative abundance of plant growth-promoting rhizobacteria such as Gemmatimonas, Devosia and Bryobacter. Spearman correlation analysis showed that the addition of alkaline CSB restored the relative abundance of rhizobacteria positively correlated with pH, such as Chitinophaga, Sphingomonas, Devosia and Pseudomonas, and thus restored the rhizosphere soil environment. This study demonstrates that 5% CSB can better alleviate the toxicity of Pb to red clover and soil. We also provide a theoretical basis for the subsequent use of beneficial bacteria to regulate the repair efficiency of red clover.

[Structural Diversity and Its Temporal Variation in the Soil Bacterial Community Under Plantations of Taxodium distichum in the Riparian Zone of the Three Gorges Reservoir Area]

The riparian zone supports important ecological functions and acts as an ecotone connecting terrestrial and aquatic areas. Soil microbes under the revegetation of woody species are crucial to the biogeochemical cycle of nutrients. Here, soil samples were collected to examine the soil microbes during different emergence phases in 2019 (May:T1, July:T2, and September:T3) in the riparian zone of the Three Gorges Reservoir, China. The variations in the bacterial community were evaluated using high-throughput sequencing. The results showed that:during the emergence phases, soil properties such as pH value (pH), ammonium nitrogen (NH₄⁺-N), and nitrate-nitrogen (NO₃^--N) and soil enzymes changed significantly(P<0.05), and soil bacterial α diversity also changed with time. Except for the Chao1 index, the richness of rhizosphere soil bacteria showed T1>T2>T3, whereas the α diversity of non-rhizosphere soil bacteria showed T3>T1>T2. The redundancy analysis (RDA) test implied that soil urease, NH₄⁺-N, pH, and NO₃^--N were the key factors structuring the microbial community. Proteobacteria and Acidobacteria were the two dominant components among the 60 phyla that were detected in the soil. Based on phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt2) prediction, metabolism was the basic function of soil bacterial communities of Taxodium distichum; in the secondary functional layer, the metabolic pathways related to carbon, nitrogen, and phosphorus mainly included amino acid metabolism, carbohydrate metabolism, lipid compound metabolism, and energy metabolism, and the relative abundance of each metabolic function had a certain time difference in different periods. These findings could help us better understand how soil microbes change after restoring vegetation in the Three Gorges Reservoir area.

Vegetation restoration of abandoned cropland improves soil ecosystem multifunctionality through alleviating nitrogen-limitation in the China Danxia

The microbial requirement for nutrient resources can be estimated by soil extracellular enzyme stoichiometry (EES) and their stoichiometries. Implementing the Grain for Green Program has significantly impacted land use and soil nutrient management in the China Danxia. However, drivers of soil microbial nutrient limitation changes in abandoned cropland (AC) remained unclear after vegetation restoration. Here, according to vector analysis, we evaluated microbial nutrient limitation by studying soil EES across vegetation restoration types (naturally restored secondary forests (NF) and artificially planted forests (AF)) with AC as a control. Results showed both NF and AF soils averaged higher C- and P- acquiring enzyme, indicating rapid C and P turnover rates after vegetation restoration. However, vegetation restoration resulted in higher C requirement for microorganisms with higher enzyme C:N and vector length. In addition, microorganisms shifted from N- (< 45°) to P-limited (> 45°) conditions with enzyme N:P less than 1 after vegetation restoration, and NF exacerbated microbial P limitation compared to AF. Decreased N limitation following vegetation restoration could be contributed to improving soil ecosystem multifunctionality. The greater variation of EES was explained by the interaction of pH, soil nutrient, and microbial biomass than by any one of these factors alone, suggesting that both abiotic and biotic factors regulate microbial nutrient limitation and microbial process. Overall, our results revealed vegetation restoration could alleviate N limitation in the China Danxia, and thus enhance soil ecosystem by regulating lower microbial N limitation, which provide insight into nutrient management strategies under ecological restoration of degraded areas.

[Coupling Relationship Between Soil Functions and Environmental Factors Along an Altitudinal Gradient: A Case Study of the Meili Mountain]

Soil respiration and extracellular enzyme activity are important components of the material cycle of mountain ecosystems and play key roles in maintaining ecosystem functions. To explore the coupling relationship between soil functions and environmental factors, the soil functional indicators, environmental factors, and effects of altitude on the soil function of 36 soil samples from 12 altitudes of the Meili Mountain were analyzed. The results showed that there were significant differences in soil respirations and enzyme activities among altitudes of Meili Mountain, and high-altitude areas had higher soil functions. Soil functions increased with altitudinal difference. PCA analysis showed that the first three axes explained 56.7%, 17.4%, and 8.7% of the variance in soil functional elevation change, respectively, indicating that the functional changes related to carbon and phosphorus were higher than those related to nitrogen. There were significant correlations between environmental factors and soil functional indicators; soil function indicators had stronger correlations with soil physicochemical properties than with climatic factors. Altitude mainly affected soil function indirectly by affecting soil physicochemical properties and climatic factors. These results have great scientific significance for improving the understanding of the material cycle and ecological function of the Meili Mountain ecosystem and provide an important reference for in-depth study of the altitude distribution pattern and evolution characteristics of the soil function of the mountain ecosystem.

Identification and Quantification of Dimethachlon Degradation Products in Soils and Their Effects on Soil Enzyme Activities

In this study, high-performance liquid chromatography-high-resolution mass spectrometry (HPLC-HRMS, Q-Exactive Orbitrap) and Compound Discoverer 3.3 were used to screen dimethachlon degradation products in soils. Four metabolites 4-(3,5-dichloroanilino)-4-oxobutanoic acid (DCBAA), 3,5-dichloroaniline (3,5-DCA), succinic acid, and muconic acid were confirmed by primary and secondary ion mass spectrometry comparisons between standards and samples. A quantitative analysis method of dimethachlon residues and four metabolites in soils was developed using HPLC-HRMS. Dimethachlon degradation in agricultural soil indoor unsterilized, sterilized, and field environments in three typical areas was measured. Dimethachlon degraded fast with a half-life of less than 1 day in three nonsterile soils. The maximum DCBAA and 3,5-DCA residues during degradation could reach 22.5-35.2% of the initial concentration of the parent dimethachlon. The metabolite DCBAA had a greater impact on soil enzyme activity than the parent dimethachlon.

Living grass mulching improves soil enzyme activities through enhanced available nutrients in citrus orchards in subtropical China

Living grass mulching (LGM) is an important orchard floor management that has been applied worldwide. Although LGM can effectively enhance soil nutrient availability and fertility, its effects on microbial-mediated soil nutrient cycling and main drivers are unclear. Meanwhile, the variation of enzyme activities and soil nutrient availability with LGM duration have been rarely studied. This study aims to explore the effects of mulching age and soil layer on enzyme activities and soil nutrients in citrus orchards. In this study, three LGM (Vicia villosa) treatments were applied, i.e., mulching for eight years, mulching for four years, and no mulching (clean tillage). Their effects on the enzyme activities and soil nutrients were analyzed in different soil layers of citrus orchards in subtropical China, i.e., 0-10, 10-20, and 20-40 cm. Compared to clean tillage, mulching for four years had fewer effects on enzyme activities and soil nutrients. In contrast, mulching for eight years significantly increased available nitrogen (N), phosphorus (P) nutrients, β-glucosidase, and cellobiohydrolase activities in the soil layer of 0-20 cm. In the soil layer of 0-40 cm, microbial biomass carbon (C), N, P, N-acetylglucosaminidase, leucine aminopeptidase, and acid phosphatase activities also increased (P < 0.05). Mulching for eight years significantly promoted C, N, and P-cycling enzyme activities and total enzyme activities by 2.45-6.07, 9.29-54.42, 4.42-7.11, and 5.32-14.91 times, respectively. Redundancy analysis shows that mulching treatments for eight and four years had soil layer-dependent positive effects on soil enzyme activities. Microbial C and P showed the most significant positive correlation with enzyme activities, followed by moisture content, organic C, and available N (P < 0.05). Available nutrients contributed almost 70% to affect enzyme activities significantly and were the main drivers of the enzyme activity variation. In summary, LGM could improve soil enzyme activities by increasing available nutrients. The promotion effect was more significant under mulching for eight years. Therefore, extending mulching age and improving nutrient availability are effective development strategies for sustainable soil management in orchard systems. Our study can provide valuable guidelines for the design and implementation of more sustainable management practices in citrus orchards.

Effect of long term application of super absorbent polymer on soil structure, soil enzyme activity, photosynthetic characteristics, water and nitrogen use of winter wheat

INTRODUCTION

Water scarcity and seasonal drought are major constraints on agricultural development globally. Super absorbent polymer (SAP) is a good amendment that can improve soil structure, increase soil water retention, and promote crop growth even with less soil moisture. We hypothesize that long term application of SAP has a better effect on soil organic carbon, soil enzyme activity, photosynthetic characteristics, yield, and water and nitrogen use than short term application.

METHODS

A long term field experiment with different application rates (0 (CK), 15 (L), 30 (M), 45 (H) kg ha^-1) of SAP was conducted at the Yuzhou water conservation agriculture base of the Henan Academy of Agricultural Sciences from 2011 to 2019.

RESULTS AND DISCUSSION

The results indicate that applying SAP increases > 0.25 mm aggregates and decreased<0.25 mm aggregates in the soil after one year (2011) and 9 years (2019) of application. In addition, soil organic carbon, soil microbial biomass carbon, soil sucrase and cellulase activities, soil water consumption, water consumption, net photosynthetic rate (Pn), leaf water use efficiency (LWUE) of wheat and yield, all increased after SAP application. SAP also boosts water use efficiency and nitrogen use efficiency. Correlation analyses show that SAP promotes the growth of wheat, and improves the utilization rate of soil water and nutrients by improving the soil structure and increasing soil organic carbon and microbial enzyme activity.

CONCLUSION

Based on our research, SAP treatment at a dosage of 45 kg ha^-1 is most effective and is thus recommended.

[Effects of Long-term Straw Returning on Fungal Community, Enzyme Activity and Wheat Yield in Fluvo-aquic Soil]

To illustrate the effects of long-term straw returning on the fungal community, soil enzyme activity, and crop yield in a fluvo-aquic soil area typical of the Huang-Huai-Hai Plain, a 10-year field experiment (established in 2010) located in Dezhou City, Shandong province, was performed, including three fertilization regimes (NF, no fertilization control; NPK, fertilization with chemical N, P, and K fertilizers; NPKS, straw returning combined with chemical N, P, and K fertilizers). This study aimed to explore the regulation mechanisms of fungal communities on soil fertility, enzyme activities, and crop yield by employing co-occurrence network and structural equation model analyses. Our results showed that long-term straw returning significantly improved soil nutrients, enzyme activity, and wheat yield. Compared with the NPK and NF treatments, soil organic matter (SOM) increased by 9.20% and 34.75%, alkali-hydrolyzed nitrogen (AN) increased by 12.03% and 39.17%, dehydrogenase (DHA) increased by 37.21% and 50.91%, β-glucosidase (β-GC) increased by 17.29% and 73.48%, and wheat production increased by 16.22% and 125.53%, respectively. Different long-term fertilization regimes did not significantly change soil fungal α-diversity but resulted in significant differences in β-diversity. Available phosphorus (AP), SOM, and AN were the main driving factors of fungal community differentiation based on redundancy analysis and hierarchical partitioning analysis. Different abundance analyses revealed significantly different fungal community compositions among fertilization regimes. The long-term NF treatment resulted in a significant enrichment of phosphate/potassium-solubilizing species (i.e., Mortierella, Aspergillus, Ceriporia, and Acremonium) and symbiotic species (i.e., Leohumicola and Hyalodendriella). The relative abundance of pathogenic fungi, namely Sarocladium, Fusarium, and Fusicolla, increased significantly in the NPK treatment. Long-term straw returning in the NPKS treatment significantly stimulated the growth of plant growth-promoting species (i.e., Pseudogymnoascus and Schizothecium) and straw-degrading species (i.e., Trichocladium and Lobulomyces). Co-occurrence network analysis showed that the fungal network was composed of four main modules; the cumulative relative abundance of module 2 was significantly increased under the NPKS treatment and showed a positive linear correlation with DHA and β-GC. The structural equation model further indicated that the wheat yield was mainly regulated by SOM, whereas species of module 2 could indirectly affect SOM and wheat yield by positively regulating DHA and β-GC. Taken together, long-term straw returning to the fluvo-aquic soil area of the Huang-Huai-Hai Plain could regulate fungal interspecific interactions, stimulate the growth of specific species groups, inhibit the activity of pathogens, increase the activity of soil enzymes, promote the accumulation of SOM, and achieve high crop yield.

[Effects of manure combined with nitrogen fertilizer on yield and quality of winter wheat and soil biological characteristics in drylands of Northwest China]

We conducted an experiment with five treatments in winter wheat of the dryland of Northwest China, i.e. 30 t·hm^-2 cow dung (M) plus different doses of nitrogen fertilizer (0, 75, 150, 225, and 300 kg N·hm^-2), denoted by M+N₀, M+N₇₅, M+N₁₅₀, M+N₂₂₅, and M+N₃₀₀, respectively. After three years of treatment, wheat yield, grain quality, and soil biological characteristics were measured in two consecutive years (2018 and 2019). The results showed that the combination of manure with nitrogen fertilizer significantly increased wheat yield compared with the manure-only treatment (M+N₀). Compared with the manure-only treatment, the combined treatments significantly increased wheat grain protein content, wet gluten, sedimentation value, and extensibility, but not for starch content. Neither wheat yield nor grain quality had significant differences among the M+N₁₅₀, M+N₂₂₅, and M+N₃₀₀ treatments, but both were prominently higher than those of M+N₇₅. Soil microbial biomass carbon (MBC) and nitrogen (MBN) reached highest in M+N₁₅₀ for both years, which were distinctly higher than those of M+N₀, M+N₂₂₅, and M+N₃₀₀. In 2018, soil β-1, 4-glucosidase, cellobiohydrolase, L-leucine aminopeptidase, β-1,4-N-acetyl glucosaminidase, and alkaline phosphatase activities in M+N₁₅₀ treatment were higher than those of other treatments. In 2019, soil enzyme activities (excluding L-leucine aminopeptidase) in M+N₁₅₀ were higher than those of M+N₀ and M+N₂₂₅. MBC significantly positively correlated with MBN, and both significantly positively correlated with the activities of cellobiohydrolase, β-1, 4-N-acetyl glucosaminidase, and alkaline phosphatase. MBN significantly positively correlated with total nitrogen content and negatively correlated with NO₃^-. Considering winter wheat yield, grain quality, and soil biological characteristics, M+N₁₅₀ was conducive to sustainable production of winter wheat in drylands of Northwest China.

Long-term organic fertilizer additions elevate soil extracellular enzyme activities and tobacco quality in a tobacco-maize rotation

Organic fertilizer is effective in improving soil quality, and promoting crop growth. Combined organic and inorganic fertilization has been proved as a more favorable way to tobacco yield and quality. However, the mechanisms underlying tobacco yield and quality under combinations of different organic and inorganic fertilizer remain unclear. We conducted a 12-year tobacco (Nicotiana tabacum L.)-maize crop rotation field experiment in Yanhe experimental station, China to examine the yields and qualities of tobacco, soil nutrients, and extracellular enzyme activities associated with carbon, nitrogen, and phosphorus cycles in response to different fertilization treatments. Five fertilization treatments (no fertilization; 75 kg N fertilizer ha^-1; 450 kg oil cake ha^-1 + 75 kg N fertilizer ha^-1; 15,000 kg pig dung ha^-1 + 60 kg N fertilizer ha^-1; 3,000 kg straw ha^-1 + 75 kg N fertilizer ha^-1) were applied to tobacco while maize was fertilized with inorganic compound fertilizers. After 12 years of tobacco-maize rotation, the results showed that organic fertilizer additions elevate tobacco yield and quality, and the soil extracellular enzymes activities. Gram-negative bacteria, actinomycetes, and total soil microbial biomass were increased by organic fertilizer additions, both plant-based (oil cake and straw) and animal-based (pig dung) organics. The levels of soil organic matter, total organic carbon, total phosphorus and available phosphorus are higher in pig dung addition treatment than oil cake and straw additions. By variance analysis with respect to fertilization treatments, organic sources differentially affected the activities of diverse soil enzymes. The redundancy analysis gave that yield and quality of tobacco leaves (upper, middle, and lower leaves) positively related to soil extracellular enzyme activities. Based on analysis of yield and quality of tobacco leaves with extracellular enzyme activities and soil nutrients, it is suggested animal-based organic fertilizer, thus pig dung, should be used in combining with chemical fertilizers to improve the quality of tobacco and soil nutrients.

[Effects of Different Vegetation Types on Soil Microbial Functional Genes and Enzyme Activities in Reclaimed Coal Mine]

Long-term coal mining has seriously damaged soil structures and ecological environments. Reclaimed vegetation could effectively improve the ecological environment. There have been many studies on soil physical-chemical characteristics and microbial community structure, but there are few on soil functional microorganisms in mining areas. In this study, soil physical and chemical properties, soil enzyme activities, and the abundance of functional genes in carbon, nitrogen, phosphorus, and sulfur cycling were determined in five reclaimed lands of different vegetation types (Platycladus orientalis, Picea asperata, Pinus tabuliformis, Pinus sylvestris, and Sabina chinensis) in the Jinhuagong mining area, Datong City, Shanxi province. The results showed that the restoration types produced significant effects on soil physical and chemical properties, soil enzyme activities, and the abundance of 75 functional genes. The highest contents of total carbon, total nitrogen, and total sulfur were in the S. chinensis site. The activities of dehydrogenase and urease were the highest in P. asperata, and the lowest alkaline protease activity was in P. asperata. The alkaline protease activity was the highest in P. sylvestrist. The abundance of functional genes in the P. asperata forest was the highest, but the diversity index was significantly lower than that in other plots, which might be due to the fact that the total abundance of ureC, acsA, and mct in P. asperata accounted for more than 52%. Soil urease was significantly correlated with the abundance of six functional genes. The β diversity of the functional microbial community was significantly different among the different vegetation types, indicating that functional genes could better explain the effects of vegetation types on microbial function. The highest and lowest integrated fertility indexes were found in the P. sylvestris and P. orientalis plots, respectively. In conclusion, soil functional genes are sensitive indicators signifying the effects of different reclamation types on soil microorganisms, and P. asperata and P. sylvestris are more suitable for reclamation in this mining area.

Development of a Preemergent Nanoherbicide: From Efficiency Evaluation to the Assessment of Environmental Fate and Risks to Soil Microorganisms

Nanoparticles based on biodegradable polymers have been shown to be excellent herbicide carriers, improving weed control and protecting the active ingredient in the crop fields. Metribuzin is often found in natural waters, which raises environmental concerns. Nanoencapsulation of this herbicide could be an alternative to reduce its losses to the environment and improve gains in its efficiency. However, there is a paucity of information about the behavior of nanoformulations of herbicides in environmental matrices. In this study, the stability of nanoencapsulated metribuzin in polymeric nanoparticles (nanoMTZ) was verified over time, as well as its dissipation in different soils, followed by the effects on soil enzymatic activity. The physiological parameters and control effects of nanoMTZ on Ipomoea grandifolia plants were investigated. No differences were verified in the half-life of nanoencapsulated metribuzin compared to a commercial formulation of the herbicide. Moreover, no suppressive effects on soil enzymatic activities were observed. The retention of nanoMTZ in the tested soils was lower compared to its commercial analogue. However, the mobility of nanoencapsulated metribuzin was not greatly increased, reflecting a low risk of groundwater contamination. Weed control was effective even at the lowest dose of nanoMTZ (48 g a.i. ha^-1), which was consistent with the higher efficiency of nanoMTZ compared to the conventional herbicide in inhibiting PSII activity and decreasing pigment levels. Overall, we verified that nanoMTZ presented a low environmental risk, with increased weed control.

The Cropping Obstacle of Garlic Was Associated With Changes in Soil Physicochemical Properties, Enzymatic Activities and Bacterial and Fungal Communities

Aims

In garlic cultivation, long-time monoculture has resulted in continuous-cropping obstacles. However, the cause has not been studied to date.

Methods

We analyzed soils from garlic fields in Pengzhou, China, to determine continuous-cropping obstacle related changes in soil physicochemical properties and enzyme activities, and in the diversity and composition of bacterial and fungal communities. Furthermore, we examined the relationships between soil properties and the bacterial and fungal communities.

Results

The soil pH and the soil catalase, urease, invertase, and polyphenol oxidase activities were lower in the cropping obstacle soil than in the healthy control soil. The richness and diversity of the bacteria were lower in the cropping obstacle soil than in the control. The bacterial and fungal communities in the cropping obstacle soil were clearly different from those in the control soil. The differences in bacterial communities between the cropping obstacle soil and the control soil were associated with differences in pH and available potassium content. The taxa with higher relative abundances in the cropping obstacle soils included potential plant pathogens and the taxa with lower relative abundances included potential plant growth promoters.

Conclusion

The enrichment of plant pathogens and the depletion of plant growth promoting fungi may have contributed to the poor growth of garlic in the cropping obstacle soil. The enzyme activity and microbial community differences were associated with acidification that was likely an important factor in the deterioration of the soil ecological environment and the garlic cropping obstacle. The results provide information to guide agricultural practices in cultivating garlic.

[Effects of Cotton Stalk Returning on Soil Enzyme Activity and Bacterial Community Structure Diversity in Cotton Field with Long-term Saline Water Irrigation]

Long-term saline water irrigation will increase soil salinity, adversely affect soil physical and chemical properties, and change the diversity of soil bacteria. Straw returning can improve the soil microenvironment and subsequently affect soil enzyme activity and bacterial community structure diversity. This experiment used two types of irrigation water salinity:fresh water (FW, 0.35 dS·m^-1) and saline water (SW, 8.04 dS·m^-1). Under each irrigation water salinity, the amount of cotton straw applied was 0 and 6000 kg·hm^-2 (represented by FWST and SWST, respectively). The results showed that:compared with those under fresh water irrigation, saline water irrigation significantly increased the soil salt, bulk density, total carbon, and available phosphorus but significantly decreased available potassium content. Under saline water irrigation, straw returning significantly increased the soil total carbon, total nitrogen, available potassium, and available phosphorus but reduced soil bulk density. Compared with those under fresh water irrigation, soil sucrase, alkaline phosphatase, and catalase activities under saline water irrigation decreased by 57.24%, 35.15%, and 3.91%, respectively, whereas urease activity increased by 26.73%. However, straw returning significantly increased sucrase, alkaline phosphatase, and catalase activities but decreased urease activity. Saline water irrigation decreased the relative abundance of Acidobacteriota, Actinobacteriota, Bacteroidota, Verrucomicrobiota, and Firmicutes and increased the abundance of Gemmatimonadota and Myxococcota. Under saline water irrigation, straw returning significantly increased the relative abundance of Actinobacteriota, Bacteroidetes, Firmicutes, Crenarchaeota, Sphingomonas, Dongia, and Steroidobacter. NMDS results also showed that saline water irrigation and straw returning changed the bacterial community structure. In conclusion, straw returning can improve soil nutrient content, reduce soil bulk density and salinity, and then change soil enzyme activity and bacterial community structure diversity. The change in soil bacterial community composition was mainly affected by soil salinity and bulk density. Therefore, straw returning can improve soil fertility and help maintain the health of soil ecosystem. This study revealed a relationship between soil enzyme activities and bacterial communities, which provides a theoretical basis and mechanism for applying cotton stalk to regulate the soil enzyme and micro-ecological environment.

Effects of perfluoroalkyl substances on soil respiration and enzymatic activity: differences in carbon chain-length dependence

Perfluoroalkyl substances (PFASs) are anthropogenic compounds that exhibit ecotoxicity when discharged into the environment, causing increasing concern. An indoor experiment was conducted to investigate the effects of perfluoroalkyl carboxylic acids (PFCAs) and PFSAs on soil respiration, sucrase activity, and urease activity at 0, 7, 14, and 28 d for perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA), and perfluorobutyric acid (PFBA), and at 14 and 28 d for perfluorooctane sulfonic acid (PFOS), perfluorohexanoic sulfonic acid (PFHxS), and perfluorobutyric sulfonic acid (PFBS). PFCAs significantly inhibited soil respiration, with a significant negative correlation between respiration and PFBA (P < 0.05) at 28 d. Sucrase activities were initially inhibited by PFCAs, and then recovered. Urease activities were inhibited by PFOA at 14 d and by PFHxA at 14 and 28 d, but not by PFBA. PFOS and PFBS briefly enhanced soil respiration. PFOS inhibited sucrase activity. PFSAs significantly decreased urease activity in a concentration- and time-dependent manner. The chain-length dependence of the ecotoxicity of PFASs varied depending on concentration and time. Toxicity demonstrated a trend of initial decrease followed by increase with carbon chain length. Our results first revealed that the chain-length dependences of PFASs were also related to concentrations and exposure time.

Effects of Different Land Use Types and Soil Depths on Soil Mineral Elements, Soil Enzyme Activity, and Fungal Community in Karst Area of Southwest China

The current research was aimed to study the effects of different land use types (LUT) and soil depth (SD) on soil enzyme activity, metal content, and soil fungi in the karst area. Soil samples with depths of 0–20 cm and 20–40 cm were collected from different land types, including grassland, forest, Zanthoxylum planispinum land, Hylocereus spp. land and Zea mays land. The metal content and enzyme activity of the samples were determined, and the soil fungi were sequenced. The results showed that LUT had a significant effect on the contents of soil K, Mg, Fe, Cu and Cr; LUT and SD significantly affected the activities of invertase, urease, alkaline phosphatase and catalase. In addition, Shannon and Chao1 index of soil fungal community was affected by different land use types and soil depths. Ascomycota, Basidiomycota and Mortierellomycota were the dominant phyla at 0–20 cm and 20–40 cm soil depths in five different land types. Land use led to significant changes in soil fungal structure, while soil depth had no significant effect on soil fungal structure, probably because the small-scale environmental changes in karst areas were not the dominant factor in changing the structure of fungal communities. Additionally, metal element content and enzyme activity were related to different soil fungal communities. In conclusion, soil mineral elements content, enzyme activity, and soil fungal community in the karst area were strongly affected by land use types and soil depths. This study provides a theoretical basis for rational land use and ecological restoration in karst areas.

[Soil Enzyme Stoichiometric Characteristics of Pinus massoniana Plantations at Different Stand Ages in Mid-subtropical Areas]

Soil enzyme activity is an important index to characterize the nutrient requirements and nutrient limitations of soil microorganisms. In this study, Pinus massoniana plantations of different stand ages (9, 17, 26, 34, and 43 a) in mid-subtropical China were taken as the research object; the activities of β-glucosidase (BG), N-acetyl-β-glucosaminidase (NAG), leucine amino-peptidase (LAP), acid phosphatase (AP), polyphenol oxidase (POX), and peroxidase (POD) were determined; and soil enzyme stoichiometric ratios were also calculated to investigate the soil microbial nutrient limitations of P. massoniana plantation development. The results showed that the activities of BG, NAG, AP, POX, and POD were enhanced with the increase in stand age, and the activity of LAP was the lowest at 17 a, which showed a significant difference and fluctuated among the neighboring stand ages. The soil enzyme C:N:P stoichiometric ratio was 1:1:0.56, which deviated from the global ecosystem enzyme C:N:P stoichiometric ratio (1:1:1). The enzyme C:N increased, whereas the enzyme N:P decreased, with increasing stand age, and both ratios tended to be stable after 17 a. There was no significant difference in enzyme N:P among different stand ages. The vector length of enzyme stoichiometry was not significantly different among the five stand ages. The vector angles increased with the increase in stand ages and tended to be stable after 17 a of stand age, but the angles were less than 45°. Redundancy analysis (RDA) revealed that soil carbon quality index and pH were the main factors influencing soil enzyme activity and the associated stoichiometric ratio. Our findings indicated that P. massoniana plantation soil microorganisms at different growth stages were all subjected to N limitation, and the N limitation was alleviated with the increase in stand age; however, the P requirement was gradually enhanced. Therefore, the management of P. massoniana plantations should take care to increase nitrogen fertilizer at the early growth stage of P. massoniana, and more phosphorus fertilizers need to be applied with nitrogen at the late growth stage in order to maintain the productivity and sustainable development of P. massoniana plantations.

[Effects of Bacillus fertilizer and agent on growth of young peach tree and soil environment under replant condition]

We analyzed the effects of Bacillus fertilizer and agent supplementation at different concentrations in the replanted soil by examining the growth of young peach trees, soil nutrients, enzyme activities, and fungal commu-nity. The aim of this study was to provide theoretical basis for alleviating peach replant diseases. One-year-old potted 'Yuanmeng' peach trees were subjected to eight treatments: replanted soil without supplementation (RS), non-replanted soil without supplementation (NS), replanted soil with 1%, 4%, 8% Bacillus fertilizer supplementation (BF₁, BF₂, BF₃), and 0.1‰, 0.5‰, 1‰ Bacillus agent supplementation (B₁, B₂, B₃), respectively. The results showed that shoot growth and root biomass under NS treatment were greater than that under other treatments, and the contents of soil organic matter, available nutrients and soil catalase activity were greatly enhanced. Peach trees treated with BF and B treatments showed better root development than RS, among which, BF₃ and B₁ treatments were the best, and B₁ treatment had similar effects as NS treatment. Compared with RS, BF and B treatments significantly increased the activities of soil catalase and urease during new shoot development, while B treatment significantly increased soil sucrase activity after the growth cessation of new shoots. Bacillus fertilizer and agent increased soil fungal diversity and the relative abundance of Ascomycota, Chaetomium and Penicillium, and decreased that of Basidiomycota. Considering the comprehensive parameters, BF₃ and B₁ showed more significant effects. In summary, our findings indicated that the supplementation of Bacillus fertilizer and agent to replanted soil could improve soil fertility, fungal community, and root development of roots, and thus provided a feasible method to alleviate peach replant diseases.

Temperature and pH mediate stoichiometric constraints of organically derived soil nutrients

It remains unclear how warming will affect resource flows during soil organic matter (SOM) decomposition, in part due to uncertainty in how exoenzymes produced by microbes and roots will function. Rising temperatures can enhance the activity of most exoenzymes, but soil pH can impose limitations on their catalytic efficiency. The effects of temperature and pH on enzyme activity are often examined in environmental samples, but purified enzyme kinetics reveal fundamental attributes of enzymes' intrinsic temperature responses and how relative release of decay-liberated resources (their flow ratios) can change with environmental conditions. In this paper, we illuminate the principle that fundamental, biochemical limitations on SOM release of C, N, and P during decay, and differential exoenzymes' responses to the environment, can exert biosphere-scale significance on the stoichiometry of bioavailable soil resources. To that end, we combined previously published intrinsic temperature sensitivities of two hydrolytic enzymes that release C and N during decay with a novel data set characterizing the kinetics of a P-releasing enzyme (acid phosphatase) across an ecologically relevant pH gradient. We use these data to estimate potential change in the flow ratios derived from these three enzymes' activities (C:N, C:P, and N:P) at the global scale by the end of the century, based on temperature projections and soil pH distribution. Our results highlight how the temperature sensitivity of these hydrolytic enzymes and the influence of pH on that sensitivity can govern the relative availability of bioavailable resources derived from these enzymes. The work illuminates the utility of weaving well-defined kinetic constraints of microbes' exoenzymes into models that incorporate changing SOM inputs and composition, nutrient availability, and microbial functioning into their efforts to project terrestrial ecosystem functioning in a changing climate.

[Effects of manure substituting chemical nitrogen fertilizer on rubber seedling growth and soil environment.]

The substitution of manure for chemical nitrogen fertilizers has great impacts on the growth of rubber seedlings and soil environment, with implications for rubber cultivation and transplantation and soil environment improvement. In this study, rubber seedlings of thermal research '7-33-97' strain were cultivated under four treatments: No fertilizer application (CK), only application of chemical fertilizer (N), manure replacing 50% chemical fertilizer (M+N), and manure replacing 100% chemical fertilizer (M). Plants parameters (including plant height, basal diameter, biomass, and chlorophyll), soil physicochemical properties (including pH, soil organic carbon and nitrogen, soil enzyme activities), and their relationships were investigated. The results showed that plant height, basal diameter, biomass, and chlorophyll content in the M+N and M treatments were significantly higher, while underground biomass and root-shoot ratio were significantly lower than those of in N treatment. Compared with CK, soil pH was significantly increased in the M treatment, decreased in the N treatment, and was not changed in the M+N treatment. Soil ammonium and nitrate content in the M+N and M treatments were significantly lower, while soil organic carbon content, the activity of β-1,4-glucosidase (BG), β-1,4-N-acetylglucosaminidase (NAG) and leucine aminopeptidase (LAP) were significantly higher than those of in N treatment. Results of correlation analysis showed that soil pH was negatively correlated with soil ammonium and nitrate content, but positively correlated with BG and NAG activities. The structural equation model analysis showed that soil pH had significant positive effects on seedling quality index, while nitrate content had significant negative effects, and soil enzyme activities had no significant effect. Those results indicated that soil pH and nitrate content were the important driving factors on the growth of rubber seedlings. The manure replacing of 50% and 100% chemical nitrogen fertilizer could promote rubber seedlings growth, improve soil environment, and promote sustainable development of rubber production in Danzhou City, Hainan Province.

Identification and Assessment of a Biocontrol Agent, Ochrobactrum intermedium I-5, for Management of Alfalfa Root Rot Caused by Fusarium tricinctum

Alfalfa root rot caused by Fusarium tricinctum is one of the most important soilborne diseases, resulting in significant losses to alfalfa agriculture worldwide. Fungicides used in management of the disease affect the environment and human health. In this study, a strain of Ochrobactrum intermedium (I-5), isolated from alfalfa rhizosphere soil, exhibited strong antifungal activity against a number of causative pathogens of alfalfa root rot and showed the strongest antagonistic activity against F. tricinctum (a longest radius/shortest radius ratio of 3.09). When applied at 10%, a filtrate of the strain liquid culture significantly reduced the spore production and germination and mycelial growth of F. tricinctum, and the inhibition rates were 76.67, 78.93, and 55.77%, respectively. Furthermore, a filtrate and suspension of the strain, when applied at 10%, reduced alfalfa root rot by >73% in repeated experiments. The strain clearly promoted the activities of invertase, urease, cellulose, and neutral phosphatase in alfalfa rhizosphere soil and significantly reduced the damage to rhizosphere soil quality attributable to alfalfa root rot. Moreover, the strain clearly promoted the growth of alfalfa without causing any evident damage to plants. The active substance produced by the strain was insensitive to heat and ultraviolet irradiation and displayed optimal efficacy at pH 8. To the best of our knowledge, this is the first study describing the use of O. intermedium for the biological control of alfalfa root rot. O. intermedium (I-5) has potential for application in the control of alfalfa root rot and improvement of the quality of cultivated alfalfa.

[Changes of soil microbial biomass carbon, nitrogen, and enzyme activities in East Dongting Lake wetlands at different water levels]

We analyzed soil quality based on soil microbial characteristics of three different vegetation types in the wetlands of East Dongting Lake, including Carex tristachya wetland (CTW), Phragmites australis wetland (PAW), and Salix babylonica wetland (SBW). The soil microbial biomass carbon (MBC), nitrogen (MBN) and enzyme activities were measured and the key influen-cing factors were analyzed during the normal, flood, and dry periods. The results showed that: 1) The amounts of MBC, MBN, and the activities of invertase and cellulase (except cellulase of dry season) in 0-10 cm were higher than those in 10-20 cm for all wetlands, while the catalase activity showed an opposite pattern. 2) The amounts of MBC and MBN and the values of MBC/TOC and MBN/TN for the 0-20 cm soil layer of each vegetation type wetland were the lowest in flood period. 3) Soil invertase activity for each vegetation type wetland in the 0-20 cm soil layer peaked in the dry period, while soil cellulase activity peaked in the normal period. The seasonal fluctuation of soil catalase activities in all wetlands were small, with activities being slightly higher in flood period than the other two periods. 4) Among different vegetation types, soil invertase activity of PAW was significantly higher than that of other vegetation types, and cellulase activity of which was the lowest in both normal and flood periods. There was no difference in these two enzymes activities among wetlands during the dry period. The highest soil catalase activity was found in CTW during normal period and in SBW during dry period, respectively, while its lowest value was in PAW during flood period. 5) Soil MBC, MBN and invertase activity were correlated positively with soil TOC, TN and TP, and negatively correlated with soil pH. The activities of soil cellulase and catalase were significantly negatively correlated with TOC, TN, TP and positively correlated with pH. It suggested that the seasonal fluctuation of water level affected soil C, N, P contents and pH values, with consequences on soil MBC, MBN and enzyme activities.

[Effects of water and nitrogen source types on soil enzyme activity and nitrogen utilization efficiency of wheat]

To provide basis for high-yield and high-efficiency of wheat production, with two wheat cultivars, 'Zhengmai 366' (strong gluten) and 'Bainong 207' (medium gluten), we investigated the effects of four nitrogen source types, ammonium chloride (NT₁), calcium nitrate (NT₂), urea (NT₃) and calcium ammonium nitrate (NT₄), applied under two water treatments, no irrigation (W₁) and irrigation at jointing and heading stages (W₂), on soil N-supplying capacity, grain yield and nitrogen utilization efficiency. The results showed that content of soil ammonium and nitrate at flowering stage decreased with increasing soil depths. Compared with the corresponding value of 'Zhengmai 366' under W₁ treatment, W₂ treatment decreased the contents of soil ammonium and nitrate in the 0-60 cm layer, and enzymes activities of urease, invertase and catalase by 10.0%, 13.3%, 7.5%, 2.8%, and 3.9%, respectively. For the two wheat cultivars, the content of ammo-nium was significantly higher under NT₁ and NT₃ treatments than that of others, while the content of nitrate under NT₂ and NT₃ treatments was significantly higher than that of others. Additionally, NT₃ and NT₄ treatments increased soil urease and invertase activities at the middle and later stages of grain filling. Compared with NT₁ treatment, NT₃ and NT₄ fertilization increased grain yield and nitrogen use efficiency of cultivar 'Zhengmai 366' by 14.9% and 20.7%, 25.6% and 13.9%, under W₂ treatment, respectively. Soil nitrate content in the 0-20 cm layer and the ammonium content in the 20-40 cm layer were positively correlated with wheat grain yield and nitrogen utilization efficiency. Under both water conditions, applying urea and calcium ammonium nitrate improved soil enzyme activity at the middle and later stages of grain filling, which was beneficial for wheat yield and nitrogen use efficiency.

Effects of Atrazine on Chernozem Microbial Communities Evaluated by Traditional Detection and Modern Sequencing Technology

Atrazine is a long residual herbicide commonly used in maize fields. Although atrazine can effectively control weeds and improve crop yield, long-term application leads to continuous pollution in the agricultural ecological environment, especially in the soil ecosystem, and its impact on soil microorganisms is still not clear. Four methods were used in the experiment to clarify the effect of atrazine on the bacterial populations of cultivated soil layers of chernozem in a cold region in different periods: high-performance liquid chromatography (HPLC), colorimetry, microplate, and high-throughput sequencing. The level of residual atrazine in cold chernozem decreased from 4.645 to 0.077 mg/kg soil over time, and the residue gradually leached into deep soil and then decreased after accumulating to a maximum value. Atrazine significantly affected the activities of urease and polyphenol oxidase activity in the soil layers at different periods but had no significant effect on sucrase and phosphatase activity. Atrazine significantly reduced the diversity of microbial carbon source utilization and total activity in soil layers of 0-10 and 20-30 cm but only reduced the diversity of microbial carbon source utilization in the 10-20 cm layer. Atrazine had no significant effect on bacterial populations (10-12 phyla, 29-34 genera), but had a slight effect on the relative abundance of various groups. Atrazine significantly reduced the diversity of bacterial populations in cultivated soil layers of chernozem in a cold region, and the diversity of bacterial populations decreased with decreased residue. This lays a foundation for guiding the safe use of herbicides on farmland in Northeast China.

Exogenous dopamine and overexpression of the dopamine synthase gene MdTYDC alleviated apple replant disease

Apple replant disease (ARD) is a soil-borne disease that leads to economic losses due to reduced plant growth and diminished fruit yields. Dopamine is involved in interactions between plants and pathogens. However, it remains unclear whether dopamine can directly stimulate defense responses to ARD. In this study, an exogenous dopamine treatment and dopamine synthetase MdTYDC (tyrosine decarboxylase) transgenic plants were used to verify the role of dopamine in treating ARD. First, 2-year-old apple trees (Malus domestica cv. Fuji), grafted onto rootstock M26, were grown in replant soils. The addition of dopamine (100 μM) to the soil promoted seedling growth and changed the accumulation of mineral elements in plants in replant soils. Such supplementation improved the activity of invertase, urease, proteinase and phosphatase under replant conditions. Sequencing analysis of 16S rDNA and internal transcribed spacer (ITS) rDNA revealed that dopamine had a slight influence on bacterial diversity but had an obvious effect on the fungal diversity in replant soils. The application of dopamine to replant soil changed the composition of bacterial and fungal communities. Second, overexpression of MdTYDC in apple plants alleviated the effects of ARD. MdTYDC transgenic lines exhibited mitigated ARD through inhibited degradation of photosynthetic pigment, maintaining the stability of photosystems I and II and improving the antioxidant system. Furthermore, overexpression of MdTYDC improved arbuscular mycorrhizal fungi colonization by improving the accumulation of soluble sugars under replant conditions. Together, these results demonstrated that dopamine enhances the tolerance of apples to ARD.

[Soil available nitrogen and phosphorus contents and the environmental impact factors across different land use types in typical karst rocky desertification area, Southwest China.]

In this study, we collected soil samples from four different land use types (forest land, shrub land, grassland and abandoned land) in Huajiang valley of Guizhou Province, a typical karst rocky desertification area in Southwest China. Correlation analysis and redundancy analysis were used to examine the distribution of available nitrogen (N) and available phosphorus (P) in diffe-rent soil layers from 0 to 30 cm and the relationships between soil environmental factors (soil physical indexes, organic carbon components, electrochemical properties, metal oxides and enzyme activities) and the contents of available N and available P. The results showed that the concentrations of soil total N, total P, available N, available P decreased significantly with the increases of soil depth. The concentrations of soil available N and available P in forest land and shrub land were significantly higher than those in grassland and abandoned land, which were significantly positively correlated with soil organic carbon composition, enzyme activity, surface electrochemical properties and amorphous mental oxide while significantly negatively correlated with soil silt and free metal oxides. Results of the redundancy analysis showed that the environmental factors affecting soil availa-ble N and available P of the four land use types were basically the same, with soil particulate organic carbon, total organic carbon and soil specific surface area playing a key role in driving the variations of soil available N and available P. The efficient explanation of variation to soil available N and P contents by soil particulate organic carbon might be due to the reduction of soil nutrient loss by the storage of N and P in organic matter. Except for high enzyme activity and electrochemical properties of forest land and shrub land, the higher soil available N and available P concentrations compared with grassland and abandoned land might be resulted from the inhibition of free iron and aluminum oxides information by higher soil organic carbon content and the reduced adsorption and fixation of N and P by iron and aluminum oxides.

[Relationships between stoichiometric characteristics of soil enzymatic activities and environmental factors in parallel valleys of western Yunnan, China.]

The valleyes of Hengduan Mountains contain the landscapes with high heterogeneity as well as high diversity of climate and vegetation types. To explore the soil cycling of four elements (C, N, P, S) across the parallel valleys of Nujiang River, Lancang River, Jinsha River and Yuanjiang River in western Yunnan, we collected top soils (0-10 cm) in forests, grasslands, and croplands. The activities of soil enzymes, including β-glucosidase (BG), β-N-acetylglucosaminidase (NAG), acid phosphatase (AP), and sulfatase (SU), which drive the soil C, N, P and S cycling, were determined. We analyzed the relationships of soil enzymatic activities and their stoichiometric characteristics with environmental factors. The activities of both AP and NAG had significant difference among different basins and different land types. The activities of AP, BG, NAG and SU were significantly positively related with each other. From southeast to northwest, the activities of BG, NAG, and SU increased with the altitude. Across all basins, the ecoenzymatic ratios of soils always ranked as AP:SU > BG:SU > NAG:SU > BG:NAG > BG:AP > NAG:AP. Compared with forest and grassland soil, cropland soils in each watershed had a higher BG:NAG and a lower NAG:AP (except Yuanjiang River basin). Moreover, AP:SU, BG:SU and NAG:SU of cropland soils were lower than those of forest and grassland in Yuanjiang River basin. However, they were higher than forest and lower than grassland in both Lancang River basin and Jinsha River basin. Soil enzyme activities and enzymatic stoichiometry were affected by physicochemical properties of soil, climate, and location, with the most contribution from soil physicochemical properties. Agricultural land use significantly affected the stoichiometry of C:N:P acquiring enzymes in soils by reducing the activity of N-degrading enzymes relative, resulting in the increases of BG:NAG and the decreases of NAG:AP. Agricultural activities had limited effects on other enzymatic stoichiometries.