Fungal pathogen diversity and composition respond rapidly to changes in plant diversity and composition

Abstract

Accumulating evidence suggests that plant pathogens play a major role in maintaining plant community diversity. Accumulation of host-specific pathogens is expected to negatively impact productivity at low plant diversity (i.e., monocultures), thereby allowing establishment of other plant species. However, in high diversity plant communities, reduced abundance of individual plant species and/or an increase in microbial diversity may inhibit pathogen accumulation and therefore facilitate plant diversity maintenance. In addition to plant diversity, increased phylogenetic distance between plant community members may also affect pathogen accumulation as pathogens are likely to be shared between closely related plant species (i.e. within family or genus). For this reason, under-dispersed plant communities with relatively closely related species are likely to encounter similar risks as monocultures. In order to better understand the ecology of plant-pathogen interactions, fungal pathogen composition was analyzed from plots planted with combinations of 18 plant species from three plant families: Poaceae, Fabaceae, and Asteraceae. Plots were planted in monoculture, 2, 3, or 6 species richness mixtures; either representing multiple families (over-dispersed) or one family (under-dispersed). Soil samples were collected 4 months after plot planting from each of the plant diversity treatments. Soil DNA was extracted, amplified for the fungal ribosomal DNA region ITS2,barcoded, and sequenced. Using bioinformatics and closed reference OTU labeling, we analyzed linear models of known fungal plant pathogens and plant species richness, as well as plant community composition. We tested whether 1) fungal pathogen diversity increases with plant species richness and phylogenetic dispersion,and 2) fungal pathogen relative abundance varies between phylogenetic groups.Therewasa positive response of fungal plant pathogen species richness toplantedspeciesrichness treatments with no effects from non-planted species richness or from phylogenetic dispersion. There were no significant responses of total fungal richness to planted species richness, non-planted species or phylogenetic dispersion. There were significant differences in fungal pathogen community composition between proportion of plant families and species within the plots. A perMANOVA comparing fungal pathogen community response to plant treatments showed significantly different fungal pathogen communities due to the proportion of Poaceae and Fabaceae but not Asteraceae. Pathogen composition also differed in response to proportion of Coreopsis tinctoria, both in the planted species treatments and realized percent cover. Total fungal community composition was not significantly different between plant families, though it was significantly different with increased proportion of planted Dalea pupurea and realized proportion of Andropogon gerardii. We identify several fungal pathogen taxonomic groups that increase or decrease in response to proportion of each plant family to investigate potential pathogen associations. The rapid response of fungal pathogens to plant treatments support previous research suggesting the major role of plant pathogens in plant community composition and can mediate productivity benefits of plant diversity.