Contrasting successional responses of soil bacteria and fungi to post-logging burn severity

Globally, forest ecosystems are increasingly impacted by natural and anthropogenic disturbances including fire, timber harvesting and land clearance. Understanding how soil bacteria and fungi are impacted by logging and burning is important for resource management, as these microbiota underpin many essential ecosystem processes such as nutrient cycling and soil formation. Using amplicon sequencing and qPCR of the bacterial 16S rRNA gene and fungal ITS1 region, we quantified the abundance, diversity, and composition of soil bacterial and fungal communities in undisturbed forest and adjacent logged and burnt sites, which included a mosaic of burning severities (unburnt, low severity and high severity burns). Our study was conducted over a 12-month time series post-burn, in the temperate wet eucalypt forests of Tasmania, Australia. We found that over this 12-month period i) after high severity burns, total abundance and diversity returned to pre-disturbance levels in bacterial communities but not in fungal communities and ii) for each disturbance severity, the composition of bacterial communities became more similar to the undisturbed reference communities over time, while fungal communities did not. We also characterised the succession of disturbance responsive taxa in logged and burnt communities, with the relative dominance of copiotrophic bacteria and fire-associated Ascomycota fungi shifting towards oligotrophic bacteria and fire-associated Basidiomycota fungi by 12-months. Further, we highlight specific taxa that respond positively or negatively to the impacts of fire disturbance and discuss the ecological implications of our findings for forest management.