Stomatal responses of tree species from the cloud forest in central Veracruz, México

Stomatal conductance is considered as a key plant response because it plays an important role in plant physiology by controlling transpiration (water status) and CO₂ assimilation, regulating plant productivity. As stomatal conductance is affected by micro-environmental and physiological variables, changes in an altitudinal gradient will have a direct effect on stomatal conductance, which can explain their ecophysiological responses. In this work we used the envelope function method to assess the effect of three climate variables (air temperature, vapor pressure difference, photosynthetically active radiation), and two physiological (leaf water potential, transpiration) on the stomatal conductance response of four tree species (Alnus acuminata, Liquidambar styraciflua, Pinus ayacahuite, and Quercus xalapensis) from the central mountain region of Veracruz, Mexico. We found that all variables influenced stomatal conductance. We also found differential stomatal conductance responses among species, where A. acuminata had the highest stomatal conductance. We also estimated the optimal temperature when the highest stomatal conductance occurs, and among the species, optimal temperature varied from 26 to 29 °C. The most sensitive species to changes in photosynthetically active radiation, leaf water potential and transpiration was L. styraciflua, and for vapor pressure difference was A. acuminata. We also proposed that the stomatal conductance response could help to explain ecophysiological responses along the elevation gradient.