Divergent changes in diversity and network complexity across different trophic-level organisms drive soil multifunctionality of fire-impacted subtropical forests

Widespread forest fires pose significant challenges to the diverse communities of soil-dwelling organisms and the multiple ecosystem functions they support. However, whether the biodiversity and interactions of various taxonomic groups respond to fire consistently in terms of direction and extent, and their relative role in regulating post-fire soil functioning, remains largely unexplored. In this study, we investigated whether the diversity and co-occurrence networks of soil organisms across various trophic levels (including bacteria, fungi, protists, and invertebrates) in subtropical forests exhibit consistent responses to fire. Furthermore, we investigated their contribution to regulating soil multifunctionality, which is measured by a range of soil extracellular enzyme activities, available nutrients and reduced potential fungal plant pathogens. Our findings revealed that fire led to a decline in the richness of fungi, protists, and invertebrates, without significantly impacting bacterial richness. Fire also simplified the microbial co-occurrence networks while complexifying the invertebrate networks. Interestingly, soil multifunctionality tended to decrease with the richness of lower-trophic communities (i.e., bacteria), whereas it increased with that of high-trophic communities (i.e., protists and invertebrates). Moreover, fire indirectly influenced soil multifunctionality by altering biodiversity and network complexity, particularly pronounced in high-trophic communities. Overall, our results underscored the divergent vulnerability of biodiversity and networks to fires across taxa groups, highlighting the crucial role of biodiversity and interactions of higher trophic taxa groups in shaping the recovery and functionality of fire-affected soils.