Drought mitigates negative effects of natural microbiomes in grasses

Research suggests that soil microbes, specifically arbuscular mycorrhizal fungi (AMFs), can help mitigate plant drought stress, but their beneficial effects on grasses are unclear. Here we test the hypothesis that soil microbes alleviate drought's negative effects on grass growth. In a greenhouse experiment, we used natural microbial inocula and eight grass species from various positions along an ecological succession gradient. Under normal watering, live soil communities decreased grass biomass, indicating a net pathogenic effect. However, this negative effect was reduced under drought compared to well-watered conditions. Amplicon sequencing revealed a significant impact of drought on rhizosphere microbial communities, particularly fungi. However, we found no evidence linking AMFs to drought stress alleviation in grasses. Our study suggests that drought reduces the negative effects of soil microbes on grass performance, regardless of successional positions. Our results also indicate that the beneficial effects of AMFs under drought are not universal, and soil biota's role in shaping plant-soil feedbacks may be less pronounced under drought conditions.