COS 195-4 - Recovery of microbial communities across a fire chrono-sequence

Background/Question/Methods

Wildfires are important and natural disturbances in forest ecosystems that drive diversity. However, the intensity and frequency of wildfires has increased in the recent decades and is predicted to continue increasing with climate change. Fires have well described effects on animal and plant communities as well as soil biochemistry. A number of studies have reported that fire reduces microbial biomass, richness, and alters composition, but also promotes the growth of fire specialist (pyrophilous) species.


The objective of this study is to determine the impacts of fire severity and depth on the soil microbiome across temporal scales. We investigated changes in microbial biomass, richness and composition across a chrono-sequence of five wildfires occurring from 2010 to 2020 in Colorado montane coniferous forests. We collected soil samples at two depths from low and high severity burned plots and unburned controls to test our hypotheses that microbes will be less resilient at shallower depths and to higher severity fire, but that microbial biomass and richness will increase with time post-fire. We used qPCR of 16S and 18S to estimate bacterial and fungal biomass and Illumina MiSeq sequencing of 16S and ITS2 amplicons to assess bacterial and fungal richness and composition.

Results/Conclusions

Our results indicate that both bacterial and fungal biomass were significantly affected by fire severity, soil depth, and time since fire. Samples from the high and low severity plots had on average lower microbial biomass than control plots. Microbial biomass was also affected by sampling depth, with shallow samples (0–5 cm deep) harboring higher biomass than deep samples (5–15 cm deep). Depth also modulates the response of microbial communities to fire severity. In shallow samples, fire severity had a significant effect on bacterial biomass in recent fires (2018-2020) but not in older fires (2010–2016). Conversely, fungal biomass in shallow samples was significantly affected by fire severity in all sites. In deep samples, bacterial biomass was not affected by severity whereas fungal biomass was affected by severity in 3 out 5 sites. These results show than bacterial biomass is more resilient than fungal biomass to fire severity and to soil depth. Analysis of impacts on bacterial and fungal richness and composition is ongoing.