Effects of grazing on soil spatial heterogeneity depend on herbivore assemblages and components of heterogeneity

The spatial heterogeneity of soil limiting resources, particularly nitrogen (N) and phosphorus (P), are vital for maintaining grassland productivity, biodiversity, and ecosystem functions. Grazing by large herbivores is a prevalent land use in grasslands, significantly modifying nutrient cycling and spatial heterogeneity. However, the differential impacts of various herbivore assemblages on the spatial heterogeneity of soil N and P, and their association with heterogeneity components (compositional and configurational heterogeneity), remain inadequately understood. Here, we conducted a 7-year field experiment in the Horqin sandy grassland of northeast China to assess the effects of different herbivore assemblages (no grazing, cattle grazing, sheep grazing, and mixed grazing of cattle and sheep) on the spatial heterogeneity of soil N and P. Our findings indicate that the effects of herbivore grazing on spatial heterogeneity of soil limiting resources are strongly dependent on herbivore assemblages and the components of heterogeneity. All herbivore species impacted soil configurational heterogeneity, while their impact on compositional heterogeneity was negligible. This suggests that grazing primarily modifies the spatial distribution patterns of limiting resources rather than altering nutrient content variability. Variation partitioning analysis revealed that herbivore grazing increased the spatial heterogeneity of soil N and P mainly by changing the plant community characteristics, such as diversity and composition, with a lesser contribution from the direct return of animal excreta. Cattle grazing significantly increased plant community heterogeneity and legume abundance, leading to increased configurational heterogeneity of all soil limiting resources, especially inorganic N. In contrast, mixed grazing and sheep grazing exhibited inconsistent effects on soil configurational heterogeneity, ranging from weak to strong spatial dependence. Our results suggest cattle grazing plays a significant role in promoting the spatial heterogeneity of both plant community and soil limiting resources in intensively managed grasslands. We emphasize that configurational heterogeneity is highly sensitive and critical for evaluating the responses of grazing on soil nutrient heterogeneity, providing valuable evidence for the spatial impacts of large herbivores on grassland ecosystems.