Linking between soil properties, bacterial communities, enzyme activities, and soil organic carbon mineralization under ecological restoration in an alpine degraded grassland

Effects of Artificial Vegetation Restoration Pattern on Soil Phosphorus Fractions in Alpine Desertification Grassland

Phosphorus (P) is essential for plant growth, but its soil availability depends on the characteristics of P fractions. However, few studies have examined soil P fractions under ecological restoration in alpine and semi-humid regions. This study investigated three restoration methods on the eastern Tibetan Plateau: planting mixed grasses (MG), planting Salix cupularis alone (SA), and planting Salix cupularis in combination with grasses (SG), restored for 14 years, with untreated sandy land (CK) as control. Through field sampling and laboratory analysis, soil P fractions and physicochemical properties were analyzed. The findings demonstrate that the three ecological restoration modes could increase total P and total organic P content and reduce inorganic P content. Ecological restoration can improve the content of soil labile P (resin-Pi, NaHCO3-Pi, and NaHCO3-Po) by activating NaOH-Pi and HCl-P, thus improving the availability of soil P and increasing the potential P (residual-P) source. Soil P fractions content positively correlated with SWC, SOC, and TN (p < 0.05) but negatively with BD and pH (p < 0.05). The experimental outcomes of this study will help to understand the P availability and its potential sources during ecological restoration while providing a scientific foundation for selecting optimal restoration strategies in alpine sandy land.

Wetland restoration suppresses microbial carbon metabolism by altering keystone species interactions

Soil bacteria play a pivotal role in regulating multifaceted functions of terrestrial ecosystems. Unraveling the succession of bacterial communities and the feedback mechanism on soil organic carbon (SOC) dynamics help embed the ecology of microbiome into C cycling model. However, how wetland restoration drives soil bacterial community assembly and species association to regulate microbial C metabolism remains unclear. Here, we investigated soil bacterial diversity, community structure and co-occurrence network, enzyme activities and SOC decomposition in restored wetlands for one, three, and four years from paddy fields in Northeast China. Wetland restoration for three and four years increased taxonomic (richness) and phylogenetic diversities by 2.39-3.96% and 2.13-3.02%, respectively, and increased the relative contribution of nestedness to community dissimilarity, indicating increased richness changed soil bacterial community structure. However, wetland restoration for three and four years decreased the richness index of aerobic Firmicutes by 5.04-5.74% due to stronger anaerobic condition characterized by increased soil Fe2+/Fe3+ from 0.20 to 0.64. Besides, wetland restoration for four years decreased network complexity (characterized by decreased node number by 2.51%, edge number by 9.62%, positive/negative edge number by 6.37%, average degree by 5.74% and degree centralization by 6.34%). Robustness index decreased with the increase of restoration duration, while vulnerability index increased with the increase of restoration duration, indicating that wetland restoration decreased network stability of soil bacterial communities. These results might be because stronger anaerobic condition induced the decrease of aerobic Bacilli richness index in keystone module, thereby reducing positive association within keystone module. Decreased positive species association within keystone module in turn weakened microbial C metabolism by decreasing hydrolase activities from 7.49 to 5.37 mmol kg SOC-1 h-1 and oxidase activities from 627 to 411 mmol kg SOC-1 h-1, leading to the decrease of SOC decomposition rate from 1.39 to 1.08 g C kg SOC-1 during wetland restoration. Overall, our results suggested that although wetland restoration after agricultural abandonment increased soil bacterial diversity, it decreased positive association within Bacilli-dominated keystone module under stronger anaerobic condition, which weakened microbial C metabolism and SOC decomposition.

The influence of rhizosphere soil microorganisms and environmental factors on gentiopicroside content in the roots and rhizomes of Gentiana scabra Bunge from Liaoning Province

Background

Rhizosphere soil microorganisms, as the second genome of plants, play an important role in the formation of secondary metabolites of medicinal plants and are one of the key factors in the formation of the authenticity of medicinal materials.

Methods

In this paper, the rhizosphere soils of Gentiana scabra Bunge from six producing areas in Liaoning Province were taken as the research objects. Through high-throughput sequencing technology, and with the help of PLS-DA and RDA, the impacts of rhizosphere soil microorganisms and environmental factors on the quality of G. scabra were explored in depth.

Results

Alpha diversity shows that the diversity of bacterial communities varies significantly, while the regularity of fungi is weak; beta diversity shows that samples from different producing areas can be effectively grouped according to community structure. LDA effect shows that the differential species of bacteria and fungi vary among different producing areas. Indicator and random forest analysis show that Sphingomonas and Subgroup_2 are the main indicator species of the bacterial communities in the high-content group, which can increase the evenness of microbial communities and maintain or enhance species diversity. The regularity of fungal communities is relatively weak. Functional metagenomic analysis shows that the functions of soil microorganisms in the six producing areas are similar but the relative abundances are different. The main functions of bacteria are closely related to microbial metabolism in diverse environments, biosynthesis of secondary metabolites, metabolic pathways, etc.; fungi are mainly lichen parasite, plant saprotroph, and ericoid mycorrhizal. PLS-DA and RDA analysis show that properly adjusting the key environmental factors of Ca, pH, and rapidly available potassium, which have a great influence on G. scabra, can affect the abundances of microorganisms such as Subgroup_2, Burkholderia-Caballeronia-Paraburkholderia, Metarhizium, Bryobacter, Fusarium, Rhodanobacter, Cladophialophora, Sphingomonas and Trichoderma, and then regulate the content of gentiopicroside.

Discussion

This study provides practical microbial approaches and strategies for improving gentiopicroside content in the roots and rhizomes of G. scabra, and lays a solid scientific foundation for ensuring the quality and safety of genuine medicinal materials and the stable and sustainable development of the G. scabra planting industry.

Impact of Different Land-Use Types on Soil Microbial Carbon Metabolism Function in Arid Region of Alpine Grassland

There are discrepancies that exist in the effects of different land uses on soil organic carbon (SOC) and soil microbial carbon metabolism functions. However, the impact of land-use type changes on soil microbial carbon metabolism in alpine grassland arid areas is not well understood, hindering our understanding of the carbon cycling processes in these ecosystems. Therefore, we chose three types of land use (continuous reclamation of grassland (RG), abandoned grassland (AG), and natural grazing grassland (GG)) to study the microbial carbon metabolism and its driving factors by the Biolog-ECO method. The results showed that the soil organic carbon content decreased by 16.02% in the RG and by 32.1% in the AG compared to the GG in the 0-20 cm soil layer (p < 0.05). Additionally, microorganisms have the highest utilization efficiency of carbohydrate carbon sources, the average values of average well color development (AWCD) were RG (0.26), AG (0.35), and GG (0.26). In the 0-20 cm soil layer, the Shannon-Wiener and the Simpson indices were 3% and 1% higher in the AG compared to the GG, respectively. The soil TOC/TN and soil available phosphorus (AP) were key factors that affected the diversity of soil microbial and carbon metabolism. They were closely related to land-use types. This study holds that abandoning grasslands accelerates the carbon metabolism of microorganisms, leading to the loss of SOC content.

Fertilizer reduction and biochar amendment promote soil mineral-associated organic carbon, bacterial activity, and enzyme activity in a jasmine garden in southeast China

Reducing chemical fertilizers and biochar amendment is essential for achieving carbon neutrality, addressing global warming, and promoting sustainable agricultural development. Biochar amendment, a carbon rich soil additive produced through biomass pyrolysis, enhances soil fertility, increases crop yield, and improves soil carbon storage. However, research on the combined effect of fertilizer reduction and biochar amendment on soil mineral associated organic carbon (MAOC) in jasmine gardens is limited. This study aims to determine if biochar can reduce industrial fertilizer usage without compromising soil quality. This study focuses on jasmine cultivation in southeastern China, employing four treatments: conventional fertilization (CK), biochar amendment without fertilizer (BA), fertilizer reduction (FR), and fertilizer reduction with biochar amendment (FRBA). The effects on MAOC, microbial abundance, and enzyme activity were investigated. The FRBA treatment significantly increased MAOC content by 19.98 % compared to CK (P < 0.05). The BA and FRBA treatments enhanced the diversity of soil bacteria, including Lactobacillus, Azospirillum, and Cutibacterium, which are associated with soil organic carbon sequestration and nutrient decomposition. The RandomForest model identified β-N-acetyl-glucosaminidase (NAG), electric conductivity (EC), β-1, 4-Glucosidase (BG), soil potential of Hydrogen (pH), soil bulk density (BD), and β-D-cellobiosidase (CBH) as key soil traits promoting MAOC accumulation (P < 0.05). The results indicate that BA and FRBA improve soil bacterial community structure, enzyme activity, and MAOC content, promoting soil carbon accumulation through environmental factors and dominant bacteria. This study encourages future fertilization protocols that enhance fertilizer efficiency and carbon storage in crop soils.

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.

pH-Related Changes in Soil Bacterial Communities in the Sanjiang Plain, Northeast China

Soil bacteria are crucial components of terrestrial ecosystems, playing an important role in soil biogeochemical cycles. Although bacterial community diversity and composition are regulated by many abiotic and biotic factors, how soil physiochemical properties impact the soil bacteria community diversity and composition in wetland ecosystems remains largely unknown. In this study, we used high-throughput sequencing technology to investigate the diversity and composition of a soil bacterial community, as well as used the structural equation modeling (SEM) method to investigate the relationships of the soil's physicochemical properties (i.e., soil pH, soil organic carbon (SOC), total nitrogen (TN), ammonium nitrogen (NH4+N), electrical conductivity (EC) and nitrate nitrogen (NO3-N)), and soil bacterial community structures in three typical wetland sites in the Sanjiang Plain wetland. Our results showed that the soil physicochemical properties significantly changed the α and β-diversity of the soil bacteria communities, e.g., soil TN, NH4+N, NO3-N, and SOC were the main soil factors affecting the soil bacterial α-diversity. The soil TN and pH were the key soil factors affecting the soil bacterial community. Our results suggest that changes in soil pH indirectly affect soil bacterial communities by altering the soil nitrogenous nutrient content.