UC Riverside

The increasing frequency and severity of wildfires worldwide have raised significant interest in understanding secondary successional and functional dynamics of post-fire microbes, bacteria, and fungi. It is well-known that wildfires alter microbial communities and the soil environments, resulting in a system dominated by pyrophilous “fire-loving” Ascomycetes and an environment rich in bioavailable nitrogen and chemically complex carbon (C), primarily in the form of highly aromatic pyrogenic organic matter (PyOM). Despite this knowledge, there is a gap in our understanding of microbial succession, their recovery rate, and whether post-fire microbes are equipped to degrade post-fire resources. To fill this knowledge gap, we performed the first fine-scale temporal study of post-fire soils, spanning 4.5 years from 17 days to 44 months, in a Southern California Chaparral ecosystem. We assessed biomass of bacteria with qPCR of 16S and fungi with 18S and richness and composition with Illumina MiSeq sequencing of 16S and ITS2 amplicons. We found that 1) wildfire decreased bacterial and fungal biomass and richness. Moreover, we found that post-fire microbes experienced rapid secondary succession, mirroring plant successional dynamics. Whereby succession was driven by putative tradeoffs in thermotolerance, colonization, and competition among dominant pyrophilous bacteria, Massilia and Noviherbaspirillum, and fungal Aspergills, Pyronema, and Penicillium. 2) Genes for PyOM degradation and N cycling increased over time, mirroring the rise in bacterial and fungal taxa within the first post-fire. Moreover, Massilia and Noviherbaspirillium exhibit distinct PyOM and N processing pathways, suggesting that specific traits related to post-fire resource acquisition and wildfire adaptation drive microbial secondary succession. 3) Bacteria demonstrated higher resistance and resilience, returning to pre-fire levels within 4.5 years due to the influence of multiple abiotic factors and vegetation recovery. In contrast, fungi had still not recovered from the effects of wildfire. Lastly, our study revealed that bacterial and fungal richness is linked to recovering vegetation and soil biogeochemistry. Together, our findings highlight the adaptability of ecological theories to soil microbes and indicate that dominant microbes likely facilitate microbial recovery during secondary succession. Our research has essential implications, such as providing long term monitoring of post-fire bacterial and fungal species, vegetation, and soil geochemical variables, while providing a list of pyrophilous bacterial and fungal taxa that could help inform ecological restoration and post-fire management strategies in global fire-affected regions.