Prescribed fire selects for a pyrophilous soil subcommunity in a northern California mixed conifer forest

Abstract

Low intensity prescribed fire is a critical strategy for mitigating the effects of catastrophic wildfires. The above-ground response to fire has been well-documented, including many ecosystem benefits associated with prescribed burning, but fewer studies have directly addressed the effect of prescribed fire on soil organisms. We aimed to understand how soil microbial communities respond to prescribed fire and to determine the ecological processes driving their dynamics. We extensively sampled four plots for 17 months in a mixed conifer forest in northern California, USA; immediately following a low-intensity prescribed fire, a higher-intensity prescribed fire, and two no-burn control plots. We found that prescribed fire significantly altered the community structure for both fungi (ITS) and bacteria (16S), which was sustained throughout the time-series. By comparing our community profiling results with a model of neutral community assembly, we found that the presence of most taxa across all experimental conditions could be explained by neutral processes. However, combining threshold indicator taxa analysis and correlation network analysis with the neutral model identified a cohort of taxa that responded deterministically to prescribed fire. The subcommunity identified through this series of analyses includes both known and new pyrophilous taxa. Beyond this, our analyses revealed network modules within postfire communities which were responsive to fire-intensity. Taken together, these results lay the foundation for building a process-driven understanding of microbial community assembly in the context of the classical disturbance regime of fire.

Soil carbon mineralization and microbial community dynamics in response to PyOM addition

“…Similar responses have been observed for some of the PyOM-responsive bacteria identified in this study in soils post-burn. Two responsive OTUs belonging to the Massilia and Gemmatimonas genera had high sequence similarity (> 99% BLAST similarity) to bacteria that were identified as pyrophilous following a prescribed burn at the site where we collected soil samples for this study (77). However, it remains unclear whether these bacteria in our study, and even in the field, increase due to actual consumption of PyOM-C. Techniques like DNA Stable isotope probing (qSIP) (78) with 13 Clabeled PyOM could help identify the bacteria actively incorporating the C in PyOM, and combining SIP with metagenomics can provide further insights into the functional roles of these incorporators (79).…”

A granular view of the traits controlling soil bacterial community reconstruction following a prescribed burn

“…Genomes belonging to phylum Gemmatimonadota have been recently found to be enriched after a prescribed burn 41 and have also been shown to respond positively to PyOM additions 42 .…”

“…4 ). Genomes belonging to phylum Gemmatimonadota have been recently found to be enriched after a prescribed burn 41 and have also been shown to respond positively to PyOM additions 42 . However, inspection of the MAG revealed the presence of very few putative PyOM degradation genes and no complete set of genes for any aromatic degradation pathway inspected in this study.…”

Impact of Prescribed Fire on Soil Microbial Communities in a Southern Appalachian Forest Clearcut

“…While low-severity fires can facilitate the rapid uptake of nutrients by intact roots to produce new above-ground biomass, greater fire severity may cause surface soils to reach lethal temperatures, temporarily reducing the influence of soil biota on nutrient fluxes. Moreover, the changes in soil properties and nutrient bioavailability brought about by fires can also have short- and long-term effects on the structure and activity of the soil microbial community (Schimel and Schaeffer, 2012; Alcaniz et al, 2018; Huffman and Madritch, 2018; Fischer et al, 2023). A reduction in microbial biomass due to heat is frequently observed in the soil surface layer (0–5 cm) following a fire (Alcaniz et al, 2018; Barreiro and Diaz-Ravina, 2021).…”