The soil microbiome contributes to the adaptation of grassland plant species to increasingly persistent precipitation...

Climate change is leading to more persistent precipitation regimes (PRs) featuring prolonged dry and wet periods in Northern Europe. Plants and plant communities can acclimatize, reducing the impact of repeated exposures to extreme PRs. We addressed the hypothesis that PR adaptations by the soil microbiome contribute to the acclimatization of plants. We used soils from grassland mesocosms exposed to a 1-d (1SPR) or a 30-d (30SPR) wet/dry cycle to investigate how soil legacy affects the response of four grassland plant species to subsequent PR events. During the 40-d experiment, 5-d PR (5PR) treatments reduced growth compared with 1-d (1PR) samples, independent of soil legacy. The 30SPR treatment altered soil fungal communities, influencing plant responses, with Plantago and Phleum showing significant stress adaptations when compared with 1SPR. Integrating genome-wide transcriptional, physiological, and biochemical analyses enabled us to propose a mechanistic model showing how soil 30SPR influences four grassland plant species by activating common mechanisms, including redox signaling pathways and stress hormones (jasmonic acid, ethylene, and abscisic acid) under 5PR. These responses lead to cell wall reinforcement through increased lignin and callose, enhancing resilience. Overall, these findings underscore the role of soil legacy in helping grassland plants adapt to potential future PR variations.