The impact of heating on leaf energy balance of Rwandan forest trees: results from an elevation gradient experiment

Variation in leaf structure and morphology impacts leaf temperature, leading to differences in leaf and canopy temperatures between species. This is a growing research area, and while the biophysical mechanisms are well described, datasets on leaf temperatures and understanding of the impact of warming on leaf thermal physiology are still developing, especially for African tropical forests. Here we present results from the Trop-heat and Rwanda-TREE projects which looked at leaf energy balance of saplings of eight species growing in common gardens at two elevations in the Nyungwe National Park. We compare leaf-to-air temperature differences for these species growing at mid and high elevation sites with mean temperatures of 22.5 °C and 17.5 °C, respectively. We then quantify how key energy-balance traits (leaf size, absorptance, stomatal conductance) change with warming, and evaluate the extent to which these traits and their temperature acclimation explain the observed leaf temperatures under higher growth temperatures. Together, this improves our understanding of the variation in leaf thermoregulation between Rwandan tree species and how leaf temperature regimes may alter under climate warming.