Contribuição da condutância estomática de grupos funcionais de plantas lenhosas na condutância do dossel em vegetação de Caatinga

Abstract

The arboreal species of semiarid regions contribute in different ways to the cooling of the canopy, considering the diversity of species and functional groups of plants. Although the vegetation-atmosphere relationship is important from the point of view of climate change, studies evaluating the contribution of caatinga functional groups to the canopy conductance are still scarce. The objective of this study was to evaluate the relation of the stomatic conductance of different functional groups of plants with the conductance of the canopy in Caatinga vegetation. The work was carried out in an area of the Caatinga, located in Fazenda Buenos Aires, Serra Talhada- PE. Two species of high wood density (WMD) and two species of low wood density (WDL) were evaluated. The meteorological data were obtained from a micrometeorological station installed in the study area and the canopy conductance was calculated. The stomatic conductance, leaf temperature and hydrous potential of xylem were evaluated. Stem samples were collected and anatomical structures of the xylem were measured. Analysis of variance of repeated measures and Tukey test with p < 0.05 were performed. Functional groups contributed differently to the canopy conductance. There was a positive relation of the canopy conductance and stomatal conductance (0.761). In the initial rainy season, the canopy conductance was 0.003 m s-1 , with the largest contribution to the canopy conductance occurring by the WMD species (150 mmol m-2 s -1 ). In the rainy season the species' stomatal conductance increased for WMD (100 to 300 mmol m-2 s -1 ) and WDL (200 to 300 mmol m-2 s -1 ). The canopy conductance also increased during the rainy season (0.02 and 0.05 m s-1 ). The water potential was higher for WDL (-1.2 MPa) and lower in WMD (-2.5 MPa) species. The WMD species presented greater amount of xylem vessels (58 mm-2 ) and wall thickness (16 ), and smaller diameter of the lumen of the xylem vessels (140 ). The WDL presented thin wall (9 ) and smaller amount of vessels (5 mm-2 ). These results show that, WMD species have strategies that favor the canopy conductance, even in the dry season, while WDL are more conservative and contribute to the canopy conductance in the rainy season. This study clarifies the importance of functional diversity for maintaining water and environmental balance in semi-arid regions, such as the Caatinga.