Multitrophic Network Complexity of Above–Belowground Communities Governs Karst Forest Ecosystem Multifunctionality

ABSTRACT In the highly heterogeneous and fragile karst forest ecosystem, existing research on single trophic levels fails to explain the maintenance of ecosystem multifunctionality (EMF). Moreover, integrated studies adopting multitrophic perspectives remain scarce. Therefore, this study focuses on investigating the driving mechanisms of multitrophic biodiversity on EMF. Our study explores the link between multitrophic diversity and EMF in karst forests, assessed the diversity of six trophic groups: plants, bacteria, fungi, protists, nematodes, and arthropods. We established both belowground and aboveground–belowground multitrophic co‐occurrence networks, concurrently assessing eight key ecosystem functions associated with material cycling and biomass production. Biodiversity (particularly that of plants, soil bacteria, and nematodes) showed significant positive correlations with EMF, and the multitrophic diversity index exhibited stronger predictive power than any single‐trophic‐level index. The topological properties of multitrophic co‐occurrence networks (such as negative edge count, edge density, centralization, and relative modularity) are significantly closely linked to EMF. Notably, the predictive and explanatory power of network complexity integrating aboveground and belowground organisms for EMF is significantly stronger than that of networks containing only soil organisms. Structural equation modeling revealed that plant diversity and multitrophic network complexity had a direct positive effect on EMF, while multitrophic diversity primarily enhanced EMF indirectly by promoting network complexity. Environmental factors, in turn, indirectly influenced EMF by modulating these biological components. Multitrophic network complexity exhibited the largest standardized total effect among all factors, highlighting its central role in maintaining EMF. We conclude that maintaining EMF in karst forests should prioritize conserving the overall complexity of cross trophic biotic interaction networks rather than focusing solely on species richness.