Spatial and seasonal variation in leaf temperature within the canopy of a tropical forest

Understanding leaf temperature (T-leaf) variation in the canopy of tropical forests is critical for accurately calculating net primary productivity because plant respiration and net photosynthesis are highly sensitive to temperature. The objectives of this study were to (1) quantify the spatiotemporal variation of T-leaf in a semi-deciduous tropical forest in Panama and (2) create a season-specific empirical model to predict T-leaf in the canopy. To achieve this, we used a 42 m tall construction crane for canopy access and monitored the microenvironment within the canopy of mature, 20-35 m tall trees of 5 tropical tree species during the wet and the dry season. T-leaf was correlated to photosynthetic photon flux density (PPFD) in the wet season but not in the dry season, possibly due to seasonal differences in wind speed, physiology, and canopy phenology. A structural equation model showed that T-leaf is best explained by air temperature (T-air) and PPFD in the wet season, whereas in the dry season, Tair alone predicted most of the variation in T-leaf. These results suggest the utility of an empirical approach to estimate Tleaf variability where simple meteoro logical data are available. This approach can be incorporated in future models of vegetation-atmosphere carbon and water exchange models of mature tropical forests with similar seasonality.