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

ABSTRACT: 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_leafin a semi-deciduous tropical forest in Panama and (2) create a season-specific empirical model to predict T_leafin 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_leafwas 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_leafis best explained by air temperature (T_air) and PPFD in the wet season, whereas in the dry season, T_airalone predicted most of the variation in T_leaf. These results suggest the utility of an empirical approach to estimate T_leafvariability where simple meteorological 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.