OOS 41-4 - Tracking the impact of wildfire on microbial carbon cycling across temporal scales

As climate change progresses, the western US is experiencing shifting wildfire behavior to more frequent and severe wildfires. Wildfires reduce soil microbial biomass and alter the community composition of the soil microbiome, selecting for “pyrophilous” taxa with encoded traits that enable them to thrive in burned soil. The soil microbiome is an often overlooked, but key player, in terrestrial ecosystems, through the mediation of carbon (C) cycling processes and the regulation of soil organic matter decomposition and stabilization. In addition to post-fire shifts in the soil microbiome, wildfire alters ecosystem C stocks by decreasing C quantity through combustion and altering C quality via fire-induced transformations to increasingly aromatic pyrogenic organic matter (pyOM). The interplay between altered microbiome function and ecosystem C dynamics across space and time remains poorly understood, and multi-omics data coupled with ecosystem models can provide a link between soil microbiome function and post-fire soil C budgets.

Here, we have compiled an extensive field-generated multi-omic dataset including 108 metagenomes and 12 metatranscriptomes from fire-impacted Colorado coniferous forests representing different burn severities (low and high severity) across varying timescales (1, 3, 5, and 11 years post-fire to multidecadal chronosequence). These sequencing efforts have resulted in 1651 metagenome-assembled genomes that span the Actinobacteria (n = 861 MAGs), Proteobacteria (n = 315), Acidobacteria (n = 115), along with 17 other bacterial phyla, all coupled to soil chemistry data. Putative pyrophilous taxa identified in previous studies are also represented, including the Actinobacteria Arthrobacter (n = 14) and Blastococcus (n = 11), and Proteobacteria Massilia (n = 9). Data from one year post-fire revealed increased genomic potential and expression of genes for degradation of catechol and protocatechuate, common intermediate aerobic degradation products of a diverse array of aromatic compounds, in severely burned soils. Longer term (up to 5 decades post-fire), the microbiome in burned soils continued to display altered genomic potential for degrading different C compounds, via genes for targeting aromatic C substrates and changes in carbohydrate-active enzyme profiles, suggesting a lasting influence of wildfire on microbially-mediated C cycling. Further work will integrate these field-generated omics insights into a widely used ecosystem model, ecosys, to quantify changes in C stocks and cycling in post-fire systems over time. Combined, this effort will help refine impacts of wildfire on soil C cycling in subalpine coniferous forest ecosystems of the western US.