Pathogen community assembly in a host population is associated with interannual variation in seasonal environmental...

The seasonal timing of pathogen development, i.e. its phenology, may be determined by host or environmental cues and shape pathogen communities. Yet, it is less clear to what degree seasonal patterns of pathogen community assembly vary over longer timescales and how strongly variation is determined by local environmental factors. This raises two general questions: how repeatable is seasonal pathogen community assembly across years? If community assembly is not repeatable, what role does environmental variation play in driving differing patterns of pathogen phenology? To address these questions, we tracked fungal pathogen prevalences in a field population of grass, tall fescue (Lolium arundinaceum) , over 3 years and used multivariate analyses to test for concordance between pathogen community assembly and seasonal environmental conditions. Ordination analyses showed that pathogen communities began at a similar community state each spring but diverged among years as the growing season progressed. To examine this, we tested for concordance between variation in the whole pathogen community structure and environmental conditions. Dissimilarity in pathogen community assembly was largely explained by interannual variation in environmental conditions, with precipitation and relative humidity being most important. Taken together, our results suggest linkages between interannual variation in environmental conditions and pathogen community assembly. This article is part of the theme issue 'Wild plant pathosystems'.