Photosynthetic capacity, canopy size and rooting depth mediate response to heat and water stress of annual and perennial grain crops

•Process-based model quantifying climate change vulnerability of perennial wheat•Plant traits drive annual-perennial differences in leaf temperature and gas exchange•Highest gas exchange in perennials with high leaf area and photosynthetic capacity•Water use and carbon fixation in a dry down depend on traits and evolving conditions•Deep roots are essential for perennials to withstand a prolonged dry down