Recent research progress of soil nematode ecology in China.

Soil nematodes are a crucial component of belowground ecosystems. Soil nematode ecology, the studies of community distribution, structural composition, ecological functions, and interaction mechanisms with environment, has always been a hot spot in soil biology research. We systematically elaborated soil nematodes' high diversity and various diet, their advantages as bioindicator and model organisms, and their roles in biological control, ecological functions and soil health. Then, we reviewed the research progress of soil nematode ecology in China, including molecular biology identification methods, responses to global changes, food web structure and function, aboveground and belowground diversity relationship, and large-scale diversity pattern. We put forward the development trend of soil nematology, focusing on the high-throughput sequencing technology in nematode identification and quantification, the necessity of establishing a universal analysis platform to promote soil nematode research, and the importance of strengthening large-scale soil nematode survey.

Long-term phosphorus fertilization reveals the phosphorus limitation shaping the soil micro-food web stability in the Loess Plateau.

The intricate decomposition pathways within soil micro-food webs are vital for cycling soil organic carbon and nutrients, influencing the quality, productivity, and sustainability of soil systems. However, the impact of diverse phosphorus addition on these organic decomposition pathways still needs to be explored. In an 8-year experiment, phosphorus (P) fertilizer was added at varying levels (0 kg ha-1, CK; 60 kg ha-1, P60; 120 kg ha-1, P120; and 180 kg ha-1, P180), to investigate the response of the soil micro-food web. The results revealed a significant effect of phosphorus addition on soil microorganisms and nematodes, with P60 exerting a greater influence than other treatments. At P60, the Shannon index of nematodes and fungi surpassed other treatments, indicating higher diversity, while the Shannon index of bacteria was lower. The Chao1 index of bacteria and fungi at P60 was higher, contrasting with the lower index for nematodes. Metabolic footprints of bacterivores and omnivores-predators (BFMF and OPMF) were higher at P60, while metabolic footprints of fungivores and plant parasites (FFMF and PPMF) were lower, signifying altered energy flow. Functional metabolic footprints and energy flow analysis unveiled a stable soil micro-food web structure at P60, with enhanced energy conversion efficiency. Network analysis illustrated positive correlations between fungi, fungivorous nematodes (FF), and omnivorous-predatory nematodes (OP) at P60, while P120 and P180 showed positive correlations among bacteria, bacterivorous nematodes (BF), and OP. Path analysis underscored the higher contribution rate of BF-C, FF-C, and OP-C to soil organic carbon at P60 compared with P120 and P180. These findings suggest that nutrient interactions between fungi and nematodes regulate soil micro-food web decomposition under low phosphorus concentrations. In contrast, interactions between bacteria and nematodes dominate at high phosphorus concentrations. The study indicates that adding phosphorus has nuanced bottom-up effects, intricately shaping the structure and activity of the pathways and underscoring the need for a comprehensive understanding of nutrient dynamics in soil ecosystems.

Heavy metal pollution triggers a shift from bacteria-based to fungi-based soil micro-food web: Evidence from an abandoned mining-smelting area.

Heavy metals pose significant threats to soil biota, ultimately disrupting soil micro-food web. However, no studies have yet elucidated the impact of heavy metals on soil micro-food web. In this study, we explored the response of bacteria, fungi, nematodes, and soil micro-food web along a gradient of heavy metals in an abandoned smelting-mining area. We found that bacteria responded strongly to heavy metals, whereas fungi showed greater resistance and tolerance. Nematodes responses were less apparent. With the increasing levels of heavy metal pollution, the importance of heavy metal-tolerant organisms in micro-food webs increased significantly. For instance, the keystone bacteria in soil micro-food web shifted from copiotrophic to oligotrophic types, while the keystone nematodes shifted from to bacterial-feeding (e.g., Eucephalobus) to fungal-feeding species (e.g., Ditylenchus). Additionally, elevated heavy metal concentrations increased the proportion of fungi (e.g., Mortierellomycota), intensifying their interactions with bacteria and nematodes and causing a shift from bacteria-based to fungi-based soil micro-food web. Furthermore, heavy metal contamination induced a more complex and stable soil micro-food web. Overall, we highlight the changes in soil micro-food web as a mechanism for coping with heavy metal stress. Our study provides valuable insights into how heavy metal pollution can cause shifts in soil micro-food webs and has critical implications for enhancing our understanding of the ecological consequences of environmental pollution at the ecosystem level.

The driving mechanism of soil organic carbon biodegradability in the black soil region of Northeast China.

The biodegradability of soil organic carbon (BSOC), defined as soil mineralization C per unit of soil organic carbon (SOC), is considered to be an important indicator of SOC stability and is closely related to the global C cycle. However, the magnitude and driving mechanism of BSOC in farmland remain largely unexplored, especially at the regional scale. Here, we conducted regional scale sampling to investigate latitude distribution pattern of BSOC and the relative contributions of biotic (soil micro-food web) and abiotic (climate and soil) drivers to BSOC in the black soil region of Northeast China. Results showed that BSOC declined with increasing latitude, which indicates that as the latitude increases, SOC becomes more stable in the black soil region of Northeast China. Over a range of latitude from 43°N to 49°N, BSOC was negatively correlated with soil micro-food web metrics of diversity (indicated by species richness), biomass and connectance, and soil factors of soil pH and clay content (CC), while it was positively correlated with climate factors of mean annual temperature (MAT), mean annual precipitation (MAP) and soil factor of soil bulk density (SBD). Among those predictors, soil micro-food web metrics were the most direct factors contributing to the variations of BSOC, which exerted the largest total effect on BSOC (-0.809). Collectively, our results provide convincing evidence that soil micro-food web metrics play a direct vital role in determining the distribution pattern of BSOC over a range of latitudes in the black soil region of Northeast China. This highlights the necessity of considering the role of soil organisms in regulating C dynamics in prediction of SOC mineralization and retention in the terrestrial ecosystem.

Variations in the soil micro-food web structure and its relationship with soil C and N mineralization during secondary succession of subalpine forests.

The soil micro-food web is an important network of belowground trophic relationships and it participates directly and indirectly in soil ecological processes. In recent decades, the roles of the soil micro-food web in regulating ecosystem functions in grasslands and agroecosystems have received much attention. However, the variations in the soil micro-food web structure and its relationship with ecosystem functions during forest secondary succession remain unclear. In this study, we investigated how forest secondary succession affected the soil micro-food web (including soil microbes and nematodes) and soil carbon and nitrogen mineralization across a successional sequence of "grasslands - shrublands - broadleaf forests - coniferous forests" in a subalpine region of southwestern China. With forest successional development, the total soil microbial biomass and the biomass of each microbial group generally increased. The significant influences of forest succession on soil nematodes were mainly reflected in several trophic groups with high colonizer-persister values (particularly bacterivore3, herbivore5 and omnivore-predator5) that are sensitive to environmental disturbance. The increases in the connectance and nematode genus richness, diversity, and maturity index indicated an increasingly stable and complex soil micro-food web with forest succession, which was closely related to soil nutrients, particularly the soil carbon contents. Additionally, we found that the soil carbon and nitrogen mineralization rates also exhibited generally increasing trends during forest succession, which had significant positive correlations with the soil micro-food web composition and structure. The path analysis results indicated that the variances in ecosystem functions induced by forest succession were significantly determined by soil nutrients and soil microbial and nematode communities. Overall, these results suggested that forest succession enriched and stabilized the soil micro-food web and promoted ecosystem functions via the increase in soil nutrients, and the soil micro-food web played an important role in regulating ecosystem functions during forest succession.

Effects of soil protists on the antibiotic resistome under long term fertilization.

Soil protists are key in regulating soil microbial communities. However, our understanding on the role of soil protists in shaping antibiotic resistome is limited. Here, we considered the diversity and composition of bacteria, fungi and protists in arable soils collected from a long-term field experiment with multiple fertilization treatments. We explored the effects of soil protists on antibiotic resistome using high-throughput qPCR. Our results showed that long term fertilization had stronger effect on the composition of protists than those of bacteria and fungi. The detected number and relative abundance of antibiotic resistance genes (ARGs) were elevated in soils amended with organic fertilizer. Co-occurrence network analysis revealed that changes in protists may contribute to the changes in ARGs composition, and the application of different fertilizers altered the communities of protistan consumers, suggesting that effects of protistan communities on ARGs might be altered by the top-down impact on bacterial composition. This study demonstrates soil protists as promising agents in monitoring and regulating ecological risk of antibiotic resistome associated with organic fertilizers.

[Structure and ecological functions of soil micro-food web.] / 土壤微食物网结构与生态功能.

Soil micro-food web, as a part of the detritus food webs, directly or indirectly participates in nutrient cycling by feeding on substrate and microorganisms and consequently influences the functions of terrestrial ecosystems. Here, we reviewed the research progress of soil micro-food web in recent years by focusing on its composition, structure and ecological function in soil ecosystem. The important roles of soil micro-food web in driving carbon (C) and nitrogen (N) transformation, organic matter decomposition and plant growth were reviewed through the description of energy channel and trophic cascade effects of soil micro-food web. At last, the research perspectives were put forward. Future researches should be combined with high-throughput sequencing and stable isotope techniques for better understanding the belowground ecological process and their feedback mechanisms to plant growth through modeling analysis.