Tree’s company: Soil fungal host preference under solo and mixed tree compositions

Steve Kutos and Elle Barnes, Biological Sciences, Fordham University, Bronx, NY, J.D. Lewis, Graduate School of Arts and Sciences - Biology, Fordham University, Armonk, NY

Background/Question/Methods
Forests and trees play critical ecological roles globally. However, trees are under stress from numerous factors including climate change and land-use change. Extensive research demonstrates that soil fungal taxa can mediate tree responses to these factors and therefore are vital to forest ecosystem function. Many factors influence the distribution of these taxa including climate, soil characteristics, and host diversity. However, the relative importance of these factors on community composition at various scales remains in question. It seems that some fungal taxa exhibit host preference in certain settings whereas others are generalists. This leads us to ask what the role of host trees on the distribution of soil fungal communities is. To address, we developed a greenhouse bioassay using saplings of three eastern tree species (Quercus rubra, Betula nigra, Acer rubrum). These saplings were planted individually and in all combinations with an added fungal inoculum from soils collected below mature field trees. At experimental end, soil fungal composition and associated function were analyzed with amplicon sequencing of the ITS1 region and fluorometric extracellular enzymatic assay. We predicted community composition would display host preference, but this preference would decrease under mixed compositions and varied communities would correlate with variation in enzymatic activity.
Results/Conclusions
We identified 1,581 ASVs dominated by the phylum Ascomycota, followed by Basidiomycota and Mortierellomycota. As expected, due to the bioassay design, there was an increase in the relative abundance of Ascomycota taxa compared to field collected soils in the area. However, there was noted compositional variation in beta diversity between each treatment. Consistent with predictions, the fungal communities varied between each of the solo sapling treatments, suggesting at least some of these taxa may have a host preference. Additionally, the data suggests that when the saplings were planted together their fungal communities became mixed with addition of taxa not found in the solo treatments. For instance, taxa from the phyla Basidiomycota and Mortierellomycota had large increases in relative abundance only in the mixed treatments. Finally, there was significantly higher potential enzymatic activity, including β-Glucosidase and acid phosphatase, among the solo treatments compared to the mixed treatments. This may be due to the increased relative abundance of saprobic fungal families found in these treatments. Overall, this study provides additional evidence of the importance of host tree identity on soil microbial communities and the potential impacts to forest functionality.