Abstract: Anthropogenic habitat fragmentation is a major driver of biodiversity loss in terrestrial ecosystems. However, its effects on species interaction networks remain poorly understood, especially for soil microbial communities. Using 23 grassland fragments within an agricultural mosaic of the agropastoral ecotone of northern China, we investigated the cascading effects of habitat fragmentation on soil microbial networks mediated by biodiversity. We found that habitat fragmentation negatively influenced soil microbial diversity and networks primarily by reducing patch area. Larger patches supported higher species richness and more complex and stable networks of soil bacteria and fungi. Habitat fragmentation induced reduced patch area had no direct effect on network complexity and stability, but indirectly decreased network complexity and stability by decreasing the species richness of soil bacteria and fungi. Our findings demonstrate that habitat fragmentation not only declines soil microbial biodiversity but also simplifies and destabilizes soil microbial networks in the agropastoral ecotone of northern China. We suggest that examining soil microbial network patterns in remnant habitats can provide valuable insights into the ecological consequences of habitat fragmentation beyond biodiversity loss.

Key words: grassland fragmentation, species-area relationship, network-area relationship, patch area, soil bacteria, soil fungi