Abstract:

Aims: Nematodes are a central component of the soil micro-food web and play a critical role in maintaining soil biodiversity and driving soil nutrient cycling and transformation processes. Although numerous studies have investigated the effects of nitrogen addition on soil fauna, a systematic understanding of how nematode communities in the litter layer and surface soil respond to nitrogen enrichment in semi-arid grassland ecosystems remains lacking. 

Methods: In this study, we conducted a field experiment in a temperate semi-arid typical steppe with four N addition levels (0, 25, 50, and 100 kg N∙ha^–1∙yr^–1), and examined the responses of nematode community diversity and ecological indices in both litter and surface soil layers to increasing nitrogen input. 

Results: We found that: (1) Compared with the surface soil nematode community, the nematode community in the litter layer was more sensitive to N addition, as evidenced by significant shifts in community structure: the dominant functional group shifted from free-living cp2 nematodes to cp1 nematodes. (2) Nitrogen addition interacted with inter-annual climatic variation to influence nematode communities, and this interactive effect was habitat-dependent. In wet years, nitrogen addition did not significantly affect nematode diversity or ecological indices in either habitat (i.e., the litter layer and surface soil). In contrast, high-level nitrogen addition during dry years significantly altered the community structure and ecological functions of nematodes in the litter layer. (3) In the litter layer, nematode community composition was significantly influenced by the aridity index, litter carbon-to-nitrogen ratio, and litter nitrogen content. In the surface soil, nematode community composition was significantly shaped by the aridity index, soil water content, and aboveground plant biomass. 

Conclusion: These findings not only provide new insights into the mechanisms driving the dynamic succession of grassland nematode communities under nitrogen deposition, but also highlight the critical role of the litter layer in maintaining the stability of belowground biotic communities.

Key words: nitrogen addition, nematode, community structure, ecological indices, typical steppe