Assembly processes and ecological network patterns of multitrophic soil mite communities in karst primary forests

Multitrophic interactions are essential for understanding the mechanisms that sustain the local coexistence of diverse soil organisms. Although stable-isotope evidence has revealed clear trophic niche differentiation among mites, co-occurrence network patterns and assembly mechanisms across trophic groups remain poorly understood. Here, we conducted a comprehensive survey of soil mites across four forest types along an elevational gradient in the Shibing World Natural Heritage Site. We aimed to elucidate the community assembly processes and ecological network complexity of predators, fungal feeders, and primary decomposers. Our results showed that community assembly processes differed among trophic groups. The assembly of fungal feeders and predators shifted from deterministic to stochastic dominance along the elevational gradient, whereas primary decomposer mites were predominantly structured by stochastic processes. Multitrophic co-occurrence networks were consistently dominated by positive associations. The α-diversity of predators showed a strong positive correlation with that of fungal feeders, and their network complexities showed a similarly positive association. Structural equation modeling indicated that mite diversity was the primary direct driver of network complexity, whereas spatial and soil attributes influenced network complexity mainly through trophic-specific indirect pathways involving diversity. These findings indicate that mite community assembly arises from the interplay between deterministic and stochastic processes, with the relative importance of these processes differing among trophic groups and along the elevational gradient. Widespread positive co-occurrence associations, potentially reflecting niche complementarity or shared habitat preferences, may further contribute to species coexistence in soil communities. In summary, our study underscores the potential importance of multitrophic mite networks in maintaining belowground biodiversity and trophic organization in karst ecosystems and provides ecological insights into belowground community assembly processes in primary karst forests.