Land-use intensification reshapes soil biodiversity via trophic-level-specific shifts in community assembly

Land-use intensification is a major driver of changes in soil biodiversity, yet the underlying community assembly mechanisms and their links to biodiversity across spatial scales remain insufficiently resolved. Here, we conducted a field survey across 30 sites in subtropical regions to quantify community assembly (stochastic versus deterministic processes, assessed using the Modified Stochasticity Ratio, MST) and α- and β-diversity of soil biota (bacteria, fungi, and nematodes) across multiple trophic levels along a land-use intensity gradient (forests, orchards, and croplands). Land-use intensification increased the contribution of stochastic processes to microbial assembly but reduced stochasticity in higher trophic groups (e.g., microbivorous and omnivorous-predaceous nematodes). Consistent with these patterns, microbial α-diversity increased, whereas both α- and β-diversity decreased for higher trophic groups. When MST was averaged across soil organisms, it was positively related to both α- and β-diversity, although the strength and direction of these relationships varied among trophic levels. Structural equation modelling further showed that declines in soil environmental heterogeneity were the dominant driver of community assembly and soil biodiversity loss at both local and regional scales. Taken together, our findings demonstrate that land-use intensification causes environmental homogenization that shifts community assembly from predominantly stochastic toward more deterministic dynamics, resulting in reduced soil biodiversity across trophic levels and spatial scales.