Higher growth temperatures compound heatwave recovery of photosynthesis in different populations of Corymbia calophylla

Global temperature rise is leading to increased stress and mortality in forests globally and is driving more frequent and intense heatwaves; however, the interaction between growth temperatures and heatwave events on tree populations remains poorly understood. We aimed to determine if gas exchange performance during and after heatwaves was determined by growth temperature, climate origin, and heatwave intensity in Corymbia calophylla saplings from four contrasting temperature-rainfall climate regions. Saplings were grown under warm and cool growth temperatures and exposed to a moderate or extreme heatwave under well-watered conditions. Upon initial heatwave exposure, saplings responded similarly in photosynthesis. Cool-grown saplings were more resilient in heatwave recovery in gas exchange traits compared to warm-grown saplings. There was some support for local adaptation in heatwave recovery with modest differences in responses between climate regions. Transpirational cooling was likely an important factor in maintaining gas exchange rates during the heatwaves and influencing recovery. These findings illustrate how a sustained increase in growth temperatures could exacerbate the effects of heatwaves in the future. This study provides insight into intraspecific variation in heatwave resistance and resilience and the role of growth temperature on performance during heatwaves.