Herbivore species and patch heterogeneity modulate grazing‐induced shifts in soil nematode trophic structure and energy flux

Grazing by large herbivores is a critical factor shaping grassland biodiversity and ecosystem functioning worldwide, yet its consequences for soil communities remain poorly understood. This gap is important because soil food webs underpin ecosystem processes and may respond differently to grazing depending on herbivore identity and local heterogeneity (i.e. patchiness). Here, a four‐year field experiment was conducted to investigate the influences of cattle and sheep grazing on soil nematode communities in a grassland that features a mosaic of degraded high‐salinity and undegraded low‐salinity patches. We focus on nematode communities because nematode‐based indices offer key insights into the structure of the soil food web and overall soil health. In the absence of grazing, degraded patches exhibited a more simplified soil food web structure, indicated by reduced nematode diversity, maturity index and structure index, but higher nematode biomass and energy flux compared to undegraded patches. However, sheep grazing reduced total nematode biomass and energy flux in degraded patches, while cattle grazing decreased the biomass of higher trophic levels (i.e. omnivores and predators), the energy flux from lower to higher trophic levels and flow uniformity in undegraded patches. These effects resulted from declines in the abundance of large‐bodied nematodes, primarily limited by soil pore space and soil microbial biomass. Collectively, our findings demonstrate that livestock grazing can exacerbate soil degradation by inhibiting soil fauna communities, but the outcomes are patch‐ and herbivore‐specific. By combining nematode structural and functional indices, our study advances understanding of how herbivore identity interacts with fine‐scale grassland heterogeneity to regulate soil food webs. This framework provides a new pathway for linking grazing management to soil health, offering a scientific basis for adaptive policies that balance production goals with sustainable grassland restoration under environmental change. Read the free Plain Language Summary for this article on the Journal blog.