Climatic drivers of oomycete communities at plant and community scales

Terrestrial oomycetes are an important, often-overlooked component of biodiversity, but their potential response to climate change remains largely unknown. We quantified oomycete communities across elevation (27–650 m) and precipitation (735–1905 mm yr⁻¹) at both a plant community and focal tree scale in above- and below-ground substrates using DNA metabarcoding. Aplanopsis, Globisporangium, Pythium, Phytophthora, and Peronospora dominated communities, with strong differentiation between above- and below-ground substrates. Oomycete presence and species richness declined with elevation in community samples, but not in focal tree samples, while community composition was strongly affected by substrate, elevation and precipitation in all sample types. Under current climate trends, our findings suggest oomycete communities at higher elevations may undergo large shifts in composition, including a 3.5 × increase in the number of oomycete species by around 2100, which could have significant consequences for plant community structure and health.