Grassland age and local adaptation shape drought resilience across semi-natural grassland populations

Increasing frequency and intensity of droughts threaten grassland ecosystems. Semi-natural grasslands vary in age from ancient to younger sites established on former arable land. While species richness and composition are known to affect drought resilience, little is known about how grassland age shapes drought responses through eco-evolutionary processes at the plant population level. We explored how grassland age and local plant-soil adaptation shape the drought resilience of plant populations by reciprocally combining soils and genotypes of a common grass, Briza media, collected from young, intermediate, and ancient grasslands - last cultivated 28-63, 63-84, and > 84-300 years ago, respectively-and subjecting the resulting mesocosms to a drought event. Ancient grassland soils enhanced drought resistance and recovery compared with younger soils. Enhanced drought resilience was primarily explained by lower abundance of putative fungal pathogens in older soils. Plants grown in 'home' soils from their sites of origin were more productive and invested less in root production to withstand water stress, indicating the important role of local plant-soil adaptation. Our results show the long-lasting legacy of land use history in soil microbial communities and their significant role in shaping drought resilience across grassland populations.