Leaf thermal regulation strategies of canopy species across four vegetation types along a temperature and precipitation gradient

The ecophysiological processes of leaves are more related to leaf temperature (Tl) than air temperature (Ta). Transpiration and leaf physical traits enable plants to maintain Tl within a thermal range. However, it is challenging to quantitatively study leaf thermal regulation strategies, due to the complex interaction between thermal effects of transpiration and leaf physical traits. We utilized a 3-T method that compares Tl, Ta, and Tn (the temperature of non-transpiring leaves) investigate thermal regulation strategies of dominant canopy species in four vegetation types, including a savanna woodland, a tropical rain forest, a subtropical evergreen broad-leaved forest, and a temperate mixed forest. Our results indicate that the difference between Tl and Ta decreased as the site mean temperature increased. Transpirational cooling was strongest in savanna woodland, and decreased from the hottest site to the coldest site. Without transpiration, sun-exposed leaves were consistently hotter under sunshine than air. This physical warming effect increased from the hottest site to the coldest site. We observed leaf area, water content and leaf angle played a significant role in physical thermal regulation. The present research quantitatively measured leaf thermal regulation strategies across a temperature and precipitation gradient, which advances our understanding of how plants adapt to their thermal environments.