Caracterização diurna e sazonal da condutância estomática de indivíduos arbóreos em resposta à variáveis ambientais na a Amazônia Central

Abstract

Understanding the interactions of the continuous soil-plant-atmosphere to ecosystem environmental changes is a prerequisite for models that predict carbon balance in tropical forests. In this context, the objective of this study was to characterize the influence of meteorological variables in the Baixio and Platô on leaf water potential (Ψf), stomatal conductance (gs) and leaf temperature (Tf) considering different techniques of two tree species, respectively in the canopy of a primary forest in Central Amazonia and to understand biochemical mechanisms such as abscisic acid production (ABA) and the relationship with stomatal regulation. The species studied were the Eschweilera cyathiformis and Pouteria anomala (in the plateau), and Peltogyne excelsa and Micropholis guyanensis (in the Baixo). The species studied in the biochemical experiment were Cariniana legalis, Handroanthus serratifolius and Astronium fraxinifolium, performed in Trancoso-BA in 2018. The meteorological variables were obtained from the instrumentation installed in two monitoring towers K34 (plateau) and B34 (Baixo). The behavior of the daily progression of Ψf of the different species in the evaluation was significant, so that the species P. anomala and E. ciathiformis in K34 is different in relation to the species P. excelsa and M. guyanensis in the Baixo, this may be related to isohydric and anisohydric behavior of the species in the plateau and shallow, respectively. For the gs dynamics of the species in response to the different rainy and dry periods there was significant difference, it was observed that gs decreased considerably in the dry period when compared to the rainy season and followed the same pattern in the plateau and shallow. The results of the measurements of Tf in the species of the basin and plateau, and for the rainy and dry periods, show significant differences so that the measurement with the porometer was more significant when compared with the techniques of Thermovisor (Flir), Thermocouples and Sensor InfraRed, as well as in relation to the air temperature measurements with Thermohygrometers. There was variation of the optimal values of Tf in the plateau relative to gs seasonally. For the entire collection period, the configuration of hysteresis behavior between stomatal conductance and VPD and Tf is obscured. In the plateau, for P. anomala, it was observed that the VPD and Tf was not sufficient to predict a greater effect on gs in the rainy season, while in the dry period VPD showed a greater effect on gs. In the Baixo, for P. excelsa and M. guyanensis, it was observed that the VPD showed to have a greater effect on gs in the rainy and dry periods. As for the biochemical experiment, it was observed that only the species Handroanthus serratifolius presented a considerable ABA concentration in the leaf and showed a diurnal variation with higher values occurring at 2:00 PM compared to the times of 12:00 AM and 6:00 PM. The concentration of ABA responded more intensely to non-irrigated treatment. Thus, speciesspecific variations in ABA biosynthesis sensitivities to environmental variables such as VPD, Tf, PAR and Ψf may help to explain the stomatal behavior of Amazonian forest species. Therefore, we conclude that environmental factors and physiological aspects alone do not explain the diurnal variation in stomatal movement. Thus, it is likely that biochemical factors such as ABA production, associated to environmental variations and their interactions with the physiology of canopy trees in the Amazon forest, are of extreme relevance to be explored to improve the understanding of how tropical forests respond to climate changes.