Wildfire strengthens the relationship between soil biodiversity and ecosystem multifunctionality in subtropical forests

Wildfires are disrupting and regenerating forces in nature that affect all ecosystem components. However, the impact of wildfires on soil multitrophic biodiversity and the resulting consequences for ecosystem multifunctionality (EMF) remain poorly understood. In this study, we sampled fire chronosequences (1-, 5-, 9-, and 27-year) from burned and unburned plots in subtropical Pinus yunnanensis forests to determine the soil biodiversity of a wide range of taxonomic groups (bacteria, fungi, protists, and nematodes), together with an extensive array of 38 ecosystem functions related to microbial activity, organic matter decomposition and mineralization, and nutrient cycling. The responses of soil biodiversity and EMF varied with soil depth and time since fire. In the surface layer (0–10 cm), a general pattern emerged in all taxonomic groups, with initial declines in soil biodiversity compared with the unburned plots, but the greatest losses occurred only at 5 years post-fire and reversed to positive in the long term. Ecosystem multifunctionality broadly followed this pattern, but the loss of EMF occurred earlier and lasted longer, indicating a lower resistance of EMF than of its supporting biodiversity. Biodiversity responses in the subsurface layer were generally weaker after an initial strong transient enhancement at 1 year. Notably, we found that regardless of the taxonomic group, fire systematically strengthened the relationship between soil biodiversity and EMF, thus promoting post-fire regeneration of EMF. This study sheds new light on the importance of biodiversity in the functioning of ecosystems in an era in which wildfire regimes are altered by global climate change.