SP08: Microbiome and stress

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Drought stress drastically changes soil properties. The reduced water availability increases oxygen availability and solute concentration, reduces diffusion rates and changes physical soil properties. Such changes induce a cascade of consequences for microorganisms. For example, reduced root exudation causes nutrient shortage for heterotrophic rhizosphere bacteria, which then reduce their metabolic activity. That might affect nutrient return to the plant. How such cascades are altered by plant diversity-induced ecosystem stability, multifunctionality or drought severity is not known and will be a central question of the proposed research. Therefore, we will investigate how drought resistant bacteria change in diversity, relative abundance and activity along plant diversity and drought intensity gradients. We will use the Y-A-S framework to classify drought resistance traits in the categories related to yield improvement (Y), nutrient acquisition (A) and stress tolerance (S). That includes bacteria able to mineralize nitrogen and phosphorus (Y-A), produce exopolsyaccharides (A-S) or osmoprotective substances (S) or those being able to become dormant (S). We will address the following research questions: 1) How does plant diversity alter the relative abundance and diversity of bacteria exhibiting different drought-tolerance traits? 2) At which drought intensity do drought-resistant bacteria (S strategy) prevail over Y-A strategists and how is that mediated by plant diversity? 3) How do drought-tolerance traits of seed and soil-derived bacteria differ? To address these questions, we will participate in the Main Experiment and the DrY Experiment, to compare long-term plant diversity effects on drought-tolerant bacteria and short-term responses to different drought severity, respectively. Additionally, we will perform a MockCoMic Experiment, which tests synthetic consortia of drought-tolerant bacteria, which are isolated from seeds and rhizosphere soils of the Main Experiment, for their effectiveness to reduce drought stress of plants. We will test (1) the relevance of microbes with different drought-tolerance traits for the plant drought resistance and recovery and (2) if it matters whether the bacteria originate from the rhizosphere soil or the seed. With our proposal, we will particularly contribute to the overarching hypothesis of the Research Unit that plant diversity stabilizes ecosystem functioning and that the long-term pattern can be predicted based on short-term responses to drought. In addition, we will be able to link functional potentials to the diversity of contributing microbial groups. This enables us to estimate whether ecosystem stability is achieved by (1) an increase of bacteria with different drought tolerance traits (multifunctionality), for example, covering the whole Y-A-S triangle or (2) by a diversification of bacterial communities with the same trait, for example, more diverse polysaccharide producers or (3) both.