Foliar pathogens and drought drive plant–soil feedback between two co-occurring herbaceous plant species

Plants alter soil biotic and abiotic properties with consequences for plant community dynamics at local and global scales, but how plant-soil interactions are affected by other environmental and biotic interactions remains poorly understood. We performed a fully reciprocal plant-soil feedback (PSF) experiment between two herbaceous plants, Monarda fistulosa and Plantago lanceolata, and tested how PSFs were influenced by drought and foliar powdery mildew pathogen infection. We observed significant negative feedbacks between the two plant species, but only when plants were grown with live soil biota and infected with powdery mildew. The strongest feedback was observed under both foliar infection and drought. High-throughput sequencing of soil fungi and bacteria from the treatment groups with foliar infection and drought revealed that both fungal and bacterial community composition were influenced by soil condition (live versus sterile) and soil training (Monarda versus Plantago). Together, our results indicate that the observed negative PSF was driven by foliar pathogens and plant species-specific soil microbial communities and intensified by drought. Our study suggests that PSF can be sensitive to both aboveground plant-pathogen interactions and climatic factors, improving our understanding of microbial impacts on plant community dynamics. This article is part of the theme issue 'Wild plant pathosystems'.