Shifts in root-associated fungal communities under drought conditions in Ricinus communis

Rhizosphere and endophytic microbial communities are crucial for plant fitness and affect how plants cope with abiotic stress. In this study, we provide evidence that drought stress affected alpha and beta diversity of fungal communities associated with the roots and rhizosphere of castor bean (Ricinus communis) through metabarcoding of 18S rRNA gene. Plants were cultivated in soil columns in the greenhouse at three different watering regimes, i.e., 50% water holding capacity (WHC; wet) or adjusted to 50% WHC every 2 weeks (dry) or every month (extremely dry). Ascomycota, Basidiomycota, Chytridiomycota and Fusarium dominated the soil and rhizosphere and Fusarium, Cladosporium, Mucor, Cystofilobasidium, Penicillium and Malassezia the roots. Under extremely dry conditions, root and rhizosphere taxonomic and functional alpha diversity increased compared to the wet treatment. However, the species turnover decreased in the stressed compared to the non-stressed roots, enriching specific fungal groups. Drought did not affect the association between castor bean and arbuscular mycorrhizal (AM) fungi. The phenolic content in stressed roots was significantly lower compared to wet conditions with a negative correlation between AM fungal colonization and root phenolic content.