Cumulative effects of large and small mammalian herbivore disturbances shift soil nematode diversity from nitrogen to phosphorus dependence across spatial scales

Mammalian herbivores regulate the stability and functioning of grassland ecosystems through grazing and diverse bioturbation behaviors. However, how multiple mammalian herbivore disturbances shape soil food web structure, nutrient cycling pathways, and the spatial organization of soil nematode are poorly understood. This study, conducted across vast alpine grasslands, examined the cumulative effects of the disturbances caused by small and large mammalian herbivores on soil nematode diversity and spatial heterogeneity. Mammalian herbivore disturbance significantly increased the alpha diversity and spatial heterogeneity of soil nematodes. Single-small-herbivore disturbance enhanced alpha diversity, whereas combined disturbances amplified stochasticity. The cumulative effects of multiple disturbance agents shifted nematode diversity from a reliance on nitrogen to a greater dependence on phosphorus across spatial scales. Additionally, mammalian herbivore disturbances diminished the positive effects of microbial diversity on the local diversity of soil nematodes. The direct and indirect effects of climate on the spatial heterogeneity of soil nematodes were strengthened by its regulation of plant functional diversity and soil properties. Plant functional traits acted as key local drivers of soil nematode spatial differentiation, with climate amplifying their effects through spatial variability in vegetation traits irrespective of disturbance type. These findings highlight the role of disturbance patterns from both large and small mammalian herbivores in shaping soil nematode diversity and nutrient cycling, with implications for alpine grassland stability and resilience.