If you can’t take the heat, move deeper in the soil: investigating the fire-tolerance of biocrust microbes

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Brianne R Palmer, Plant Science, University of California, Davis, San Diego, CA; Biology, San Diego State University, San Diego, CA and David Lipson, Department of Biology, San Diego State University, San Diego, CA

Background/Question/Methods
Fires are a common ecological disturbance and there is a need to understand how all aspects of the ecosystems recover. We assessed the recovery of biological soil crusts after a prescribed fire in 2017 and a wildfire in 2012 using field, laboratory, and bioinformatic techniques. We found that in this system, the cover of the biocrusts in the burned plots surpassed those in the unburned plots and had similar functional capacity and microbial communities. We hypothesized that this rapid colonization may be due to the survival of some microorganisms deeper in the soil surface that led to the subsequent colonization. To test this hypothesis, we collected 10cm soil cores with and without biocrusts and burned the cores with a simulated fire at 450C of 600C with controls. We then cultured the phototrophic bacteria, often the initial colonizers of biocrusts, at each centimeter depth on BG-11 plates.
Results/Conclusions
Cyanobacteria, eukaryotic algae, and bryophytes grew on plates from the 2cm level to the 10cm level for both fire temperatures and both soil types (with and without biocrusts) indicating that some biocrust forming organisms can survive simulated fire in the deeper soil layers. Although this study does not confirm that soil microbes living below 2cm depths will recolonize the surface and form biocrusts, it demonstrates a potentially viable hypothesis for explaining the rapid recovery of biocrusts in coastal grasslands. Future work will analyze the active microbial community after each fire using RNA sequencing and explore other mechanisms of biocrust recovery and restoration.