Nitrogen deposition alters soil micro-food web structure and energy flux patterns along the cold-temperate to temperate forest gradient in Northeast China

Nitrogen deposition exerts a crucial control over the functioning and stability of soil ecosystems. However, the mechanisms by which it governs the organization of the soil micro-food web and energy flux in forest soils across different climate zones remain unclear. Therefore, we conducted a nitrogen deposition simulation experiment over more than a decade across three representative forest ecosystems (the Greater Khingan cold-temperate forest, the Lesser Khingan transitional forest spanning cold-temperate to temperate zones, and the Changbai temperate forest) to investigate the impacts of nitrogen deposition on the soil micro-food web and energy flux. We examined the community structure, abundance, and biomass of soil nematodes and microbes, and analyzed the structural patterns of the soil micro-food web and energy flux. Our findings showed that nitrogen addition suppressed soil nematode abundance and biomass, reduced microbial community biomass and soil nematode community diversity. Nitrogen addition reduced the energy flux of the soil micro-food web, particularly that of predatory-omnivorous nematodes. The increase in the concentration of available nitrogen ions after soil acidification and its harmful impact on soil organisms were the main factors driving the modifications in soil micro-food web organization. Therefore, this study provides key evidence for understanding energy transfer in forest soil micro-food web under long-term nitrogen deposition and offers a theoretical basis for evaluating its effects on forest soil ecosystem stability and function.