Biology subjects

Johnson, D. B.

Publications and source records attributed to Johnson, D. B..

4 recordsLinked to original sources

bioRxiv2025

Resilience not yet apparent in soil fungal communities of the boreal forest from one to five years after wildfire across a severity gradient

Wildfires are natural disturbances characteristic of boreal forests. However, fire regimes around the world are changing, with effects on fire frequency and fire severity. Here, we present data from one and five years post-fire across 40 different sites from the boreal forest of the Northwest Territories and Alberta, Canada, asking the following questions: (1) Do the factors that structure post-fire soil fungal communities change over time? (2) Is there evidence for resilience in fungal community composition across different burn severities? (3) Do fire-enriched taxa change one vs. five years post-fire? Factors correlated with fungal community composition remain largely the same five years post-fire, with a declining correlation with burned/unburned, and an increasing association with vegetation community composition. This suggests that the immediate effects of fire on fungal community composition wane or diverge with time, while the influence of longer-term effects of fire, such as changes in vegetation, increases. Fungal communities failed to demonstrate resilience in community composition five years post-fire, in contrast to our findings for bacterial communities, and suggesting that fungal communities may be more closely tied to soil properties and vegetation communities that take longer to recover post-fire. Finally, we identify and classify fire-responsive fungi into different response types, based on their enrichment or depletion one vs. five years post fire. Persistent fire responders include taxa from the genera Penicillium, Coniochaeta, and Calyptrozyma, and the family Venturiaceae, but different taxa within a single genus respond differently to fires, underscoring that generalizations even at relatively fine taxonomic levels may be inappropriate, and that the mere presence of traits that may be relevant to post-fire success are insufficient alone to guarantee post-fire abundance. Future manipulative and observational studies will help us continue to dissect the multiple factors and traits structuring fungal responses to fires.

microbiology↗

bioRxiv2024

Effects of fire and fire-induced changes in soil properties on post-burn soil respiration

BackgroundBoreal forests cover vast areas of land in the northern hemisphere and store large amounts of carbon (C) both aboveground and belowground. Wildfires, which are a primary ecosystem disturbance of boreal forests, affect soil C via combustion and transformation of organic matter during the fire itself, and via changes in plant growth and microbial activity post-fire. Wildfire regimes in many areas of the boreal forests of North America are shifting towards more frequent and severe fires driven by changing climate. As wildfire regimes shift and the effects of fire on belowground microbial community composition are becoming clearer, there is a need to link fire-induced changes in soil properties to changes in microbial functions such as respiration in order to better predict the impact of future fires on C cycling. ResultsWe used laboratory burns to simulate boreal crown fires on both organic-rich and sandy soil cores collected from Wood Buffalo National Park, Alberta, Canada, to measure the effects of burning on soil properties including pH, total C, and total nitrogen (N). We used 70-day soil incubations and two-pool exponential decay models to characterize the impacts of burning and its resulting changes in soil properties on soil respiration. Laboratory burns successfully captured a range of soil temperatures that were realistic for natural wildfire events. We found that burning increased pH and caused small decreases in C:N in organic soil. Overall, respiration per gram total (post-burn) C in burned soil cores was 16% lower than in corresponding unburned control cores, indicating that soil C lost during a burn may be partially offset by burn-induced decreases in respiration rates. Simultaneously, burning altered how remaining C cycled, causing an increase in the proportion of C represented in the modelled slow-cycling vs. fast-cycling C pool as well as an increase in fast-cycling C decomposition rates. ConclusionsTogether, our findings imply that C storage in boreal forests following wildfires will be driven by the combination of C losses during the fire itself as well as fire-induced changes to the soil C pool that modulate post-fire respiration rates. Moving forward, we will pair these results with soil microbial community data to understand how fire-induced changes in microbial community composition may influence respiration.

ecology↗

bioRxiv2022

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

Globally, wildfires represent major disturbances, burning millions of hectares annually. Wildfires can restructure soil microbial communities via changes in soil properties and microbial mortality. Fire-induced changes in bacterial communities may influence soil carbon cycling, and recovery to pre-burn community composition and function may take years. We investigated carbon cycling, soil properties, and the importance of three fire-adaptive strategies - fire survival, fast growth, and affinity for post-fire soil environmental conditions - in structuring soil bacterial communities following burns of varying temperatures in boreal forest soils. To identify taxa with each strategy, we simulated burns and incubated soils, tracking respiration and sequencing DNA and rRNA. We then quantified their abundances in the field following wildfires of varying burn severities. The importance of these strategies varies over time and with burn severity. Fire survival has a small but persistent effect on structuring burned soil communities. Fast growing bacteria rapidly colonize the post-fire soil but return to pre-burn relative abundances between one and five years post-fire. Taxa with an affinity for the post-fire environment thrive post-fire, but the effect of this strategy declines by five years post-fire, suggesting that other factors such as vegetation recovery or bacterial dispersal may influence community composition over decadal timescales. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/495025v1_ufig1.gif" ALT="Figure 1"> View larger version (53K): org.highwire.dtl.DTLVardef@f6cf22org.highwire.dtl.DTLVardef@198f5fdorg.highwire.dtl.DTLVardef@13de0f2org.highwire.dtl.DTLVardef@17b4712_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2022

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

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.

ecology↗