Friday, August 16, 2019
Exhibit Hall, Kentucky International Convention Center
Glade A. Dlott, Department of Biology, Stanford University, Stanford, CA and Kabir Peay, Stanford University
Background/Question/Methods: Fungi co-exist with vast and diverse populations of prokaryotes in terrestrial soils. Together, these communities control the fate of most root exudates and play strong roles in both maintaining soil fertility and mediating plant-soil feedbacks. However, these microbes are usually studied at scales orders of magnitude greater than that of their interactions and community dynamics (Vos et al., 2013; Baveye et al., 2018). This study investigated the influence of sampling scale on both 1) measurements of α- and β-diversity of bacterial and fungal communities, and 2) inter-kingdom interaction between individual species, by investigating bulk soils and individual Coast Live Oak (
Quercus agrifolia) rhizosphere aggregates across a landscape. Microbial communities were analyzed using Illumina sequencing of fungal (ITS) and bacterial (16S) amplicons. We expected that aggregate microbes would represent members of actively interacting communities, while bulk soils would contain a more diverse non-interacting meta-community. We hypothesized that microbial α-diversity would be lower in individual aggregates than that of bulk soils, and that stronger patterns of co-occurrence between individual fungal and bacterial species would be observed in aggregates. Further, we hypothesized that specific consortia of bacteria and fungi might be observed in aggregates, suggesting symbiotic specificity in bacterial-fungal interactions.
Results/Conclusions: Contrary to our first hypothesis, fungal and bacterial α-diversity (Shannon) did not significantly differ between aggregate and bulk communities. This may indicate that functional redundancy and microbial hyperdiversity are common even on clusters of individual root aggregates no larger than 5 mm. We observed significant co-occurrence patterns between individual members of several mycorrhizal fungal genera (Amanita, Russula, Cortinarius) and uncultured bacteria (phylum Proteobacteria). Contrary to our second hypothesis, these were strongest within bulk soils, and much weaker in aggregates. This may indicate stronger commensal or mutualistic bacterial-fungal relationships in bulk soils compared to the rhizosphere, where competition for plant exudates is extreme. Together, these findings support the efficacy of common soil sampling methods in microbial ecology, but suggest that further research at the microscale (<250 μm) is needed to understand the mechanisms structuring bacterial-fungal interactions in soils.
