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 questions on two themes: which factors control bacterial community composition during post-fire recovery, and how does the importance of different fire-responsive traits change during post-fire recovery? We find the following: 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). 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. 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. 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.

野火可能对生态系统造成重大干扰，包括地下土壤微生物群落。此外，世界许多地方的火灾状况正在发生变化，改变并经常增加火灾的严重性、频率和规模。加拿大北部的北方森林和针叶林平原生态区的特点是 40-350 年自然发生的森林替代野火。我们之前在 40 个地点研究了火灾一年后野火对土壤微生物群落的影响，涵盖了一系列烧伤严重程度。在这里，我们在火灾发生五年后回到相同的地点，以检验一系列关于火灾对细菌群落组成影响的假设。我们就两个主题提出问题：火灾后恢复期间哪些因素控制细菌群落组成，在火灾后恢复过程中，不同火灾响应特征的重要性如何变化？我们发现：火灾后五年，植被群落、水分状况、pH、总碳、质地和燃烧/未燃烧都仍然是具有相似预测值的细菌群落组成的重要预测因子（R² )。在火灾发生五年后，细菌群落变得更类似于未燃烧的地点，在严重程度范围内，表明具有复原力，而共生网络的一般结构在火灾发生一年和五年后保持相似。使用预测的 16S rRNA 拷贝数估计的快速生长潜力不再与火灾后五年的烧伤严重程度显着相关，这表明该特征对于构建细菌群落组成的重要性可能仅限于相对较短的时间尺度。许多在火灾后一年在燃烧地点富集的分类群在火灾后五年仍然富集，尽管它们的富集程度普遍下降。来自Massilia、Blastococcus和节杆菌都保持显着富集，这表明它们可能具有允许它们在火灾后环境中继续繁衍的特征，例如对增加的 pH 值的耐受性或降解热原有机物的能力。这项基于假设的工作扩大了我们对土壤细菌群落火灾后恢复的理解，并提出了新的假设以在未来的研究中进行测试。