Functional identity shapes oomycete community assembly across native grassland plants

This study investigates how plant functional identity structures the diversity and specialization of soil-borne oomycete communities in native Canadian grasslands. Using a paired rhizosphere–bulk soil sampling design, we profiled oomycete assemblages associated with four dominant native species spanning key functional groups: two grasses (Calamovilfa longifolia, Nassella viridula), a forb (Linum lewisii), and a legume (Dalea purpurea). Amplicon sequencing of the mitochondrial cox2 locus revealed distinct host-associated patterns in oomycete composition and guild structure. Grasses supported compositionally similar, phylogenetically clustered assemblages dominated by generalist Pythium and Globisporangium taxa, consistent with rapid root turnover and spatial escape from infection. In contrast, the forb and legume hosted more compositionally variable and specialized communities enriched in Aphanomyces and Lagenidium, lineages indicative of resource- or defence-mediated selection. Across all hosts, we observed substantial unclassified diversity, suggesting cryptic or under-sampled oomycete lineages and functional redundancy within grassland soils. These findings demonstrate that host functional traits, such as root architecture and nutrient economy, govern oomycete community assembly and may underpin negative plant–soil feedbacks that stabilize coexistence in prairie ecosystems.