Resilience in soil bacterial communities of the boreal forest from one to five years after wildfire across a severity gradient

Abstract

Wildfires can represent a major disturbance to ecosystems, including soil microbial communities belowground. Furthermore, fire regimes are changing in many parts of the world, altering and often increasing fire severity, frequency, and size. The boreal forest and taiga plains ecoregions of northern Canada are characterized by naturally-occurring stand-replacing wildfires on a 40-350 year basis. We previously studied the effects of wildfire on soil microbial communities one year post-fire across 40 sites, spanning a range of burn severity. Here, we return to the same sites five years post-fire to test a series of hypotheses about the effects of fire on bacterial community composition. We ask the following questions: (1a) Do the fundamental factors structuring bacterial community composition remain the same five years post-fire? (1b) Do the effects of fire on bacterial community composition decrease between one and five years post-fire? (1c) Do shifts in bacterial community composition between one and five years post-fire suggest resilience? (2a) Does the importance of fast growth diminish between one and five years post-fire? (2b) Do short-term post-fire responders continue to dominate the community five years post-fire? We find the following: (1a) Five years post-fire, vegetation community, moisture regime, pH, total carbon, texture, and burned/unburned all remained significant predictors of bacterial community composition with similar predictive value (R2). (1b and 1c) Bacterial communities became more similar to unburned sites five years post-fire, across the range of severity, suggesting resilience, while general structure of co-occurrence networks remained similar one and five years post-fire. (2a) Fast growth potential, as estimated using predicted 16S rRNA copy numbers, was no longer significantly correlated with burn severity five years post-fire, indicating the importance of this trait for structuring bacterial community composition may be limited to relatively short timescales. (2b) Many taxa that were enriched in burned sites one year post-fire remained enriched five years post-fire, although the degree to which they were enriched generally decreased. Specific taxa of interest from the genera Massilia, Blastococcus, and Arthrobacter all remained significantly enriched, suggesting that they may have traits that allow them to continue to flourish in the post-fire environment, such as tolerance to increased pH or ability to degrade pyrogenic organic matter. This hypothesis-based work expands our understanding of the post-fire recovery of soil bacterial communities and raises new hypotheses to test in future studies.

An empirical approach to developing and testing a traits-based fire ecology framework for bacterial response to wildfires

“…We quantified the total relative abundance of taxa assigned to each of the strategies using our laboratory experiments in a dataset of natural wildfires in the same region [8, 73]. Briefly, soils were collected from organic and mineral horizons in the field, one year and five years post-fire, across a range of burn severities including unburned sites, and spanning the same vegetation communities and soil types from which cores were collected for the laboratory experiments.…”

Rapid bacterial and fungal successional dynamics in first year after Chaparral wildfire

“…Currently, most research evaluating post-fire microbiomes is based on single timepoint sampling (Dove & Hart, 2017; Pressler et al, 2019); thus, the succession of pyrophilous microbes is nearly unknown. However, recent research consisting of 2-3 sampling time points suggests that bacteria and fungi experience rapid post-fire community changes (Ferrenberg et al, 2013; Qin & Liu, 2021; Whitman et al, 2022), indicating that higher temporal resolution sampling is needed to understand bacterial and fungal successional trajectories.…”