Plant-soil feedback responses to drought are species-specific and only marginally predicted by root traits

Background and aims: The increasing occurrence of extreme drought events under climate change alters the composition and functioning of plant communities worldwide. Drought-induced changes in plant-soil feedback (PSF), reciprocal effects on fitness between plants and their associated soil microbial communities, are one mechanism through which these changes in vegetation occur, but they remain difficult to predict. Because of their direct link to rhizosphere microbial communities, we expect root traits to predict drought-induced PSF shifts. 

Methods: In the conditioning phase of a greenhouse experiment, we subjected 12 common grassland species to drought. In the feedback phase, all species were grown under ambient conditions with their own microbial inoculum. Their growth was compared to growth in sterile soil to assess total PSF or soil inoculated with microbes from three other species to assess specific PSF. We used root traits to predict PSF under drought and ambient conditions. 

Results: Drought altered the magnitude and direction of PSF in a quarter of the species, which was consistent between total and specific PSF. Total PSF was best predicted by the first axis of the root trait space (high specific root length to high root diameter and root nitrogen content) and was not responsive to drought. Specific PSF was weakly predicted by root traits and changed in response to drought. 

Conclusion: Our results show that drought can modify the feedbacks between plants and their microbial communities with implications for vegetation dynamics. Root traits have limited capacity to predict these shifts, but can predict PSF of the total microbial community independent of drought.