Land use is a determinant of plant pathogen alpha- but not beta-diversity.

Little is known about the diversity patterns of plant pathogens and how they change with land use at a broad scale. We employed DNA metabarcoding to describe the diversity and composition of putative plant pathogen communities in three substrates (soil, roots, and leaves) across five major land uses at a national scale. Almost all plant pathogen communities (fungi, oomycetes, and bacteria) showed strong responses to land use and substrate type. Land use category could explain up to 24% of the variance in composition between communities. Alpha-diversity (richness) of plant pathogens was consistently lower in natural forests than in agricultural systems. In planted forests, there was also generally low pathogen alpha-diversity in soil and roots, but alpha-diversity in leaves was high compared with most other land uses. In contrast to alpha-diversity, differences in within-land use beta-diversity of plant pathogens (the predictability of plant pathogen communities within land use) were subtle. Our results show that large-scale patterns and distributions of putative plant pathogens can be determined using metabarcoding, allowing some of the first landscape level insights into these critically important communities.