Functional Biogeography of Soil Microbial eDNA of different Fire-Associated Areas in the Angeles National Forest

Background/Question/Methods

: Wildfires have increased in frequency and severity due in part to climate change (CARB). To improve understanding of microbial soil communities’ response to fire in the Angeles National Forest, Gold Creek Preserve, we performed two rounds of soil sampling. Sampling took place during winter 2020 and summer 2021 (38 samples total). Sequencing libraries were prepared with 16S, FITS, 18S, 12S, PITS, and COI amplicons. Data were analyzed using QIIME2, ranacapa, and mixomics. Ranacapa was used for multivariate ANOVA and alpha diversity analysis. Mixomics was used to conduct sparse partial least squares analysis (sPLS). We hypothesized that the different areas of the preserve would have differential abundance of taxa associated with their fire histories. We hypothesized the Blue Trail, a wildlife corridor which burned in the 2017 Creek fire, would have the highest alpha diversity of fungal taxa and the highest F:B (fungi: bacteria) ratio. The Red Trail was burned in the 2009 Station Fire and the Creek Fire, and the Creek Fire and 2016 Sand Fire affected the Green Trail. We also endeavored to explore other factors which may have influenced microbial communities, such as soil classification and plant host.

Results/Conclusions

: Communities showed significant differences in composition in different fire areas of the Preserve. The highest F:B was related to the Green Trail. The Chi-square test revealed differences in F:B proportions between different trails (p=2*10^-16). Plant rootzone was not significantly associated with alpha/beta diversity of the communities based on PERMANOVA and observed species. However, in sPLS, moderate associations (r >0.5) showed between plant, topography, soil/sediment, soil classification, latitude, and suites of taxa. Strong associations (r >0.8) existed between longitude, elevation, and clusters of taxa. sPLS was sensitive to outliers; results focused on a cluster of Green Trail samples with high elevation and longitude. Analysis revealed the cluster included the post-fire pioneer fungus Pyronema, Tremella and Strobiloscypha, and Chlorellales algae. Potentially pathogenic Fusarium sequences were elevated. Corallococcus, which secretes antimicrobials, and bacterivorous Spumella were associated with the cluster. In the clusters of variable-associated taxa, there was functional redundancy. Clusters were differently composed, but shared similar ecological functions. These results imply a set of traits for post-fire resiliency. These included photo-autotrophy, mineralization of pyrolyzed organic matter and aromatic or oily compounds, pathogenicity and parasitism, antimicrobials, digestion of microbes, and N-metabolism.