Soil enzyme activity and stoichiometry in secondary grasslands along a climatic gradient of subtropical China

Organic carbon and nitrogen accrual evidenced by the underpinning protection mechanisms in soil profile following contrasting 35-year fertilization regimes

Soil organic matter (SOM) is a highly complex variable and needs fractionation into distinct pools based on their differing behaviour to better elucidate and predict its dynamics. The present study aimed to quantify the soil organic carbon (SOC) and total nitrogen (TN) stocks and assess their sensitivity indices in fractions with contrasting functionality. Furthermore, the correlations were also evaluated between SOC and TN stocks of pools, system grain yield (SGY), soil physico-chemical properties, and climatic variables. The results demonstrated that C and N stocks in the combined application of organic manure (M), and nitrogen, phosphorus, and potassium (NPK) i.e., MNPK and sole application of M treatments significantly augmented at 0-40 cm and 40-100 cm soil layers, respectively. Also, the SGY was significantly higher under all fertilization treatments than control (no fertilization). Furthermore, SOC and TN stocks of major soil fractions were positively correlated with soil nutrients and mean annual precipitation. Thus, long-term manure application integrated with mineral fertilization (MNPK) in Black soil or Mollisol leads to enhanced crop yields and pool-associated SOC and TN stocks up to 40 cm depth. Whereas the manure-alone (M) is critical for enhancing pool-associated SOC and TN stocks at 40 to 100 cm soil profile. This study implicated how the SOC and TN stocks in different fractions respond to manure and mineral fertilization (35 years) which is pivotal for improving SOC and TN sequestration by modulating the response of SOM pools. The results provide insights into the accrual of C and N stocks underpinned by the stabilization mechanisms specifically implying the significance of microaggregation across the soil profile of cropland.

Artemisia argyi leaf powder improves soil properties and recruits Sphingobium bacteria to promote the growth and yield of Pinellia ternata

Recent research has reported the strong herbicidal activity of Artemisia argyi leaf powder (AALP), indicating its high potential for use as an environmentally friendly weed management solution for ecological agriculture. However, AALP's impacts on soil physicochemical properties and microbial communities have remained uninvestigated. This study explores these effects through pot experiments assessing the AALP's efficacy in weed suppression and its ability to promote the growth of Pinellia ternata, a plant utilized in traditional Chinese medicine. The results demonstrate that a 10% concentration of AALP suppressed nearly 100% of all weeds. Additionally, AALP treatments at 2.5%, 5%, 7.5%, and 10% concentrations increased P. ternata yields by 29.79%, 24.76%, 35.67%, and 31.00%, respectively. A soil analysis revealed that AALP enhanced soil fertility by increasing the contents of nutrients such as SOM, AN, AP, AK, Ca, Fe, Mn, and Zn, as well as the enzyme activity of CAT, ACP, UE, and SC, creating an optimal growth environment for P. ternata. In addition, AALP significantly increased the PA (phenolic acid) content in soil, which is a key factor in inhibiting weed germination and growth. Furthermore, a microbial community structure analysis indicated an enrichment of Actinobacteriota and Bacteroidota after AALP treatment, with notable increases in the growth-promoting bacteria Sphingobium and Flavobacterium. A permutational multivariate analysis of variance (PERMANOVA) based on the Bray-Curtis distance reaveled that all of the tested soil properties were significantly correlated with changes in bacterial community composition except for pH. Further two-factor correlation network analysis identified AN, Zn, SC, and PA as key environmental factors. Finally, the Sphingobium sp. strain AFR15, isolated from AALP-treated soil, exhibited significant growth-promoting effects on P. ternata. After inoculation with Sphingobium sp. strain AFR15 for one month, the heights of P. ternata were increased significantly. The leaf length and leaf width of P. ternata were also positively correlated with the treatment concentration of AFR15, and the chlorophyll contents of the leaves also increased. This results highlighted Sphingobium sp. strain AFR15's potential as a specialized microbial fertilizer in crop yield increased. In conclusion, AALP applications not only control weeds but also promote P. ternata growth by improving soil physiochemical properties and fostering beneficial bacterial allies. These findings lay the groundwork for future research and promote the use of AALP in ecological agriculture.

Effect of Compound Fertilizer on Foxtail Millet Productivity and Soil Environment

The effects of balanced fertilization with nitrogen, phosphorus, and potassium (NPK) on foxtail millet productivity and the soil environment under the same conditions of total nutrients have received limited research attention. Therefore, in this study, three balanced fertilization patterns of 27-14-10 (T1), 27-17-7 (T2), and 30-10-11 (T3), and one no fertilization treatment (CK), a total of four treatments, were set up through a two-year field experiment to study the effects of balanced fertilization patterns on foxtail millet yield and soil environment. Mantel analysis was conducted to reveal the correlation between soil environmental factors and the community and their contribution to productivity. The results showed that: (1) all balanced fertilization treatments significantly increased foxtail millet yield, with the highest yield in the T1 treatment. (2) The contents of EC, available K, available P, and alkaline-hydrolyzable nitrogen in the soil of the two-year TI treatments were higher than those of the other treatments and increased by 7.20-9.36%, 24.87-52.35%, 55.83-56.38%, and 21.05-43.95%, respectively, compared with CK. (3) Soil urease activity in the T1 treatment increased significantly by 26.67% and 9.00% compared with the control over the two years. Sucrase activity increased by 36.27% and 23.88% in the T1 treatment compared to CK, and glutaminase activity increased by 33.33% and 19.23% in the T1 treatment compared to CK. (4) T1 treatment significantly increased the OUT number and diversity index of the soil bacterial community. (5) Mantel analysis and principal component analysis showed that available soil nutrients and soil enzymes were positively correlated, and soil enzymes and soil nutrients contributed more to foxtail millet productivity. In this study, the 27-14-10 balanced fertilization pattern was more effective, providing a theoretical basis for the research and development of special fertilizers for foxtail millet and offering technical guidance for realizing the light simplified cultivation of foxtail millet and sustainable development of cost-saving and increased efficiency.

Effects of climate warming on soil nitrogen cycles and bamboo growth in core giant panda habitat

Climate change can pose a significant threat to terrestrial ecosystems by disrupting the circulation of soil nitrogen. However, experimental analyses on the effect of climate change on soil nitrogen cycles and the implications for the conservation of key wildlife species (i.e., the giant panda, Ailuropoda melanoleuca) remain understudied. We investigated the effects of a 1.5 °C, 3 °C, and 4.5 °C temperature increase on nitrogen distribution in different soil layers of bamboo forest via an in-situ experiment and assessed the implications for the growth and survival of arrow bamboo (Bashania faberi), a critical food resource for giant pandas. Our results showed that warming treatments generally increased soil N content, while effects differed between surface soil and subsurface soil and at different warming treatments. Particularly an increase of 1.5 °C raised the subsurface soil NO3-N content, as well as the content of N in bamboo leaves. We found a significant positive correlation between the subsurface soil NO3-N content and the N content of arrow bamboo. An increase of 3-4.5 °C raised the content of total N and NO3-N in the surface soil and led to a reduction in the total aboveground biomass and survival rate of arrow bamboo. Limited warming (e.g., the increase of 0-1.5 °C) may promote the soil N cycle, raise the N-acetylglucosaminidase (NAG) enzyme activity, increase NO3-N in subsurface soil, increase the N content of bamboo, and boost the biomass of bamboo - all of which could be beneficial to giant panda survival. However, higher warming (e.g., an increase of 3-4.5 °C) resulted in mass death of bamboo and a large reduction in aboveground biomass. Our findings provide a cautiously optimistic scenario for bamboo forest ecosystems under low levels of warming over a short period of time, but risks from higher levels of warming may be serious, especially considering the unpredictability of global climatic change.

Leaf carbon, nitrogen, and phosphorus ecological stoichiometry of grassland ecosystems along 2,600-m altitude gradients at the Northern slope of the Tianshan Mountains

Ecological stoichiometry of terrestrial ecosystems has been a hot issue in current research, with intense focus on the proportional relationships of nutritional elements within plants and between plants and their environment. To clarify these relationships along continuous environmental gradients is essential for a more comprehensive understanding how plants adapt to a changing environment. In arid regions, the varying plant and soil types along altitude gradients offer a unique opportunity to examine the vertical spectrum of plant and soil ecological stoichiometry. In this study, the northern slope of the Tianshan Mountains was selected as the study area to explore the carbon (C), nitrogen (N), and phosphorus (P) ecological stoichiometric characteristics of herbaceous plants along 900-m-3,500-m altitude gradients. We also investigated the variation of ecological stoichiometric characteristics among different grassland types. The results indicated that the mean C, N, and P in leaf of grassland were 342.95 g·kg-1-557.73 g·kg-1, 6.02 g·kg-1-20.97 g·kg-1, and 0.71 g·kg-1-3.14 g·kg-1, respectively. There was no significant change in leaf carbon content along the elevation gradient, and the highest and lowest leaf C concentrations were in the upland meadow and the semidesert grasslands. Both N and P concentrations obtained their highest value in the meadow steppe. The P concentration gradually increased in desert and semidesert grasslands and reached the highest value in the meadow steppe, and then decreased to the lowest value in the upland meadow and subsequently increased in the alpine meadow. The ranges of the C:N ratio, C:P ratio, and N:P ratio were 16.36-155.53, 109.36-786.52, and 2.58-17.34, respectively. Due to fluctuations in the P concentration, the C:P ratio and N:P ratio reached the lowest value in the meadow steppe and obtained their highest value in the upland meadow. Redundancy analysis showed that temperature was the dominant factor affecting the C, N, and P ecological stoichiometry of herbaceous plants, followed by soil organic carbon, mean annual precipitation, soil pH, and soil electrical conductivity. Corresponding results could enhance predictive models of nutrient cycling and ecosystem responses to climate change, particularly in arid and semiarid regions.

Soil enzyme activity mediated organic carbon mineralization due to soil erosion in long gentle sloping farmland in the black soil region

Soil erosion plays a crucial role in soil organic carbon (SOC) redistribution and mineralization. Meanwhile, the soil extracellular enzymes (EEs) drive C mineralization. However, the response of soil EEs mediated SOC mineralization to soil erosion remains unclear. We investigated the SOC and soil EEs distribution in long gentle sloping farmland (LGSF) under slop-ridge tillage (SRT) and cross-ridge tillage (CRT) in the black soil region (BSR) of northeast China. The results indicated that the SOC mineralization at the upper slope position was higher than that on the toe-slope (133 % ∼ 340 %) under CRT. However, for SRT, SOC mineralization on the back-slope was 126 % and 164 % higher than on the summit- and shoulder-slope. The SOC, dissolved organic carbon (DOC) content, and β-glucosidase (BG) activities underwent spatial migration and deposition in the lower region under both tillage practices. As for CRT, the SOC content of the back-slope was 19.21 % higher than on the summit-slope, while the DOC content at the back-slope was 29.20 % higher than on the toe-slope. The BG activity was the highest at the toe-slope, followed by the foot-and back-slope, which were 41.74 %-74.73 % higher than at the summit-slope. As for SRT, the SOC, DOC, and BG activities on the back-slope were significantly higher than other slope positions (P < 0.05). The SOC on the back-slope were 47.82 % and 31.72 % higher than those on the summit- and shoulder-slope, respectively. The DOC and BG on the back-slope were 10.98 % and 67.78 % higher than on the summit-slope. The soil EES results indicated strong C and P limitation. Spatial differences in soil C distribution resulted in a significant positive correlation between C limitation and mineralization. This indicated that soil C and nutrient distribution under different slope positions driven by soil erosion, leading to soil nutrient limitation, is a key factor influencing spatial differences in C sources or sinks.

Soil ecoenzyme activities coupled with soil properties and plant biomass strongly influence the variation in soil organic carbon components in semi-arid degraded wetlands

Wetland degradation can induce alterations in plant biomass, soil properties, and soil ecoenzyme activities, consequently influencing soil organic carbon components. Despite extensive investigations into the relationships among plant characteristics, soil properties, and soil organic carbon components, the enzymatic mechanisms underlying changes in soil organic carbon components, particularly the impact and contribution of ecoenzyme activities, remain poorly understood. This study compared the soil organic carbon components at a depth of 0-20 cm in wetlands in the semi-arid western Songnen Plain under different degradation levels and explored plant biomass, soil properties, and soil ecoenzyme activities. The results showed that the soil total organic carbon, labile organic carbon, and recalcitrant organic carbon contents in the degraded wetlands were generally lower than those in the non-degraded wetlands. Furthermore, the soil nutrient contents and soil β-1,4-glucosidase, L-leucine aminopeptidase, and acid phosphatase activities were also lower in the degraded wetlands than in the non-degraded wetlands. Vector analysis of enzymatic stoichiometry revealed that wetland degradation did not increase microbial carbon limitation. The soil organic carbon components showed significant positive correlations with plant biomass, soil water content, soil total nitrogen, soil total phosphorus, as well as soil ecoenzyme activities. Variation partitioning analysis revealed that plant biomass, soil properties, soil ecoenzyme activities collectively accounted for 78.5 % variation in soil organic carbon components, among which plant biomass, soil properties, soil ecoenzyme activities, and their interactions explaining 4.2 %, 8.0 %, 7.9 %, and 24.5 % of the variation, respectively. Therefore, the impact of soil ecoenzyme activities and soil properties on soil organic carbon component changes was greater than that of plant biomass, with the interaction of these three factors playing a crucial role in soil organic carbon formation. This study provides a theoretical basis for scientifically evaluating the carbon sink function of degraded wetland soil and preserving the wetland soil carbon pool.

Soil extracellular enzyme stoichiometry reveals the nutrient limitations in soil microbial metabolism under different carbon input manipulations

Changes in the quality and quantity of litter and root inputs due to climate change and human activities can influence below-ground biogeochemical processes in forest ecosystems. However, it is unclear whether and how much aboveground litter and root inputs affect soil microbial metabolism and nutrient limitation mechanisms. In this study, according to a 4-years field manipulation experiment, litter and root manipulations (control (CK), double litter input (DL), no litter (NL), no root (NR), and no inputs (NI)) were set up to analyze the extracellular enzyme activities and stoichiometric ratios characteristics of 0-10 cm and 10-20 cm soils, explore the metabolic limitations of microorganisms, and clarify the main driving factors restricting nutrient limitation. The results showed that the enzyme activities associated with the C cycling (β-1,4-glucosidase (BG), cellulose disaccharide hydrolase (CBH)) and N cycling (β-1,4-N-acetylglucosaminidase (NAG), leucine aminopeptidase (LAP)) in DL treatment were significantly higher than those in NR treatment. Moreover, enzyme activities related to P cycling are significantly higher in comparison to other treatments. The acid phosphatase (AP), which is related to the P cycle, showed the highest activity under NR treatment. In addition, there was no significant difference in soil microbial metabolic limitation by the different carbon inputs, which did not change the original nutrient limitation pattern. The main drivers of microbial nutrient metabolic limitation included soil physicochemical properties, soil total nutrients, and available nutrients, among which soil SWC and pH presented the greatest influence on microbial C limitation and soil total nutrients showed the greatest influence on microbial N limitation. Changes in soil carbon input altered soil extracellular enzyme activities and their stoichiometric ratios by affecting soil physicochemical properties, total nutrients. This study provides data for the understanding of material cycling in forest ecosystems under environmental change.

Effects of Cinnamomum camphora coppice planting on soil fertility, microbial community structure and enzyme activity in subtropical China

Cinnamomum camphora (C. camphora) is a broad-leaved evergreen tree cultivated in subtropical China. Currently, the use of C. camphora clonal cuttings for coppice management has become popular. However, the effects of C. camphora coppice planting on soil abiotic and biotic variances remained unclear. In this study, we collected soil from three points in the seven-year C. camphora coppice planting land: under the tree canopy (P15), between trees (P50), and abandoned land (Control) to investigate the effects of C. camphora coppice planting on soil fertility, microbial community structure and enzyme activity. The results revealed that C. camphora coppice planting significantly increased soil fertility in the point under the tree canopy (P15) and point between trees (P50), and P15 had more significant effects than P50. Meanwhile, in P15 and P50, soil bacterial, fungal alpha-diversity were improved and microbial community structures were also changed. And the changes of soil organic carbon and total nitrogen promote the transformation of soil bacterial, fungal community structures, respectively. In addition, C. camphora coppice planting significantly (p < 0.05) increased soil urease (UE), polyphenol oxidase, and peroxidase activities, while significantly decreased soil ACP activity. This study demonstrated that the C. camphora coppice planting could improve soil fertility in subtropical China, which promoted the transformation of soil microbial community from oligotrophs (K-strategist) to copiotrophs (r-strategist). Thus, this work can provide a theoretical basis for soil nutrient variation and productive management of C. camphora coppice plantation in subtropical China.