ECOPHYSIOLOGICAL RESPONSES OF NATIVE AND EXOTIC YOUNG TREES TO DROUGHT AND RAINFALL

Abstract

The ecophysiological response to drought and recovery after rainfall was evaluated for three young tree species native to México (Fraxinus uhdei, Tabebuia rosea and Ehretia latifolia) and three exotic species native to humid tropical environments (Koelreuteria paniculata, Schinus terebinthifolius and Ligustrum lucidum), all of them used to reforest the city of Guadalajara, Mexico. In May, daily net CO₂ assimilation was 133 % higher in native species (84 mmol CO₂ m^-2 d^-1) than in the exotic species (79 mmol CO₂ m^-2 d^-1). Photosynthesis in F. uhdei and T. rosea was less affected by adverse atmospheric conditions that prevailed in May, compared with the other species in study. In June, the daily net CO₂ assimilation recovery observed in response to rain was higher in the exotic L. lucidum (318 %) than in the native T. rosea (65 %). The lower values of relative water content were recorded in May for S. terebinthifolius (64 %), E. latifolia (67 %) and F. uhdei (69 %). The relative water content increased gradually in the rainy season and all species showed values of relative water content close to or greater than 90 %, and this increment was associated with increases in the daily net CO₂ assimilation DNA. The lower values of daily net CO₂ uptake and chlorophyll observed in May might be attributed to the low relative humidity (17 %) and high values of temperature (26 °C) and radiation (51 mmol m^-2 d^-1).