Grasses, legumes and forbs respond differently to compound drought-heatwave events during establishment

Abstract Aims Climate change threatens agriculture worldwide, and grasslands must adapt to withstand and mitigate the effects of extreme climatic events. While plant diversity may boost resilience, grassland responses to compound drought-heatwave (CDHW) events remain unclear. As young plants are particularly vulnerable to stress, this study investigated the effects of climate extremes during grassland establishment. Methods Two successive CDHWs, simulating average spring and summer stresses in western Europe, were applied to newly established plants from distinct functional groups: perennial ryegrass ( Lolium perenne L.), white clover ( Trifolium repens L.), and chicory ( Cichorium intybus L.). Additionally, drought and heatwave components of CDHWs were tested separately to estimate their effects. Climate-controlled growth chambers ensured precise control of environmental conditions, allowing for accurate measurements of plants'morphological and physiological responses. Results Yield responses to CDHW were driven by significant interaction among species, climate, and stress timing. Summer CDHW events reduced yields in white clover and chicory by 73% and 38%, respectively, with drought as the primary driver of stress. This trend was reversed with the occurrence of two successive CDHWs, resulting in an average 22% higher yield compared to summer CDHW alone, highlighting the importance of stress timing and recurrence in priming plants. Notably, chicory yield increased by 45% under spring CDHW conditions compared to control. Conclusion This study underscores the importance of diversifying grassland systems to enhance resilience to climate change. It provides insights into the responses of different species to CDHW events, which can guide the design of multi-species mixtures for the future.