Sazonalidade do fluxo de seiva em árvores nativas de dois grupos funcionais da Caatinga

Abstract

Understanding the dynamics of water flows is important to predict vegetation responses to climate change, given the predictions of increased intensity of prolonged droughts in the tropics. Within this context, the responses of plants of different functional groups to the seasonality of rain, may indicate the resistance and resilience of species in drought conditions. Although research has explored pulse dynamics in arid and semi-arid regions, few studies have been conducted in seasonally dry tropical forests. The caatinga represents an exemplary ecosystem to study the plant response to drought, due to its extreme seasonality. Therefore, the objective of this work was to relate the seasonal dynamics of water in the plant through the flow of sap and phenological aspects of species representing two functional groups in the Brazilian semiarid region. For the installation of sap flow sensors (Js), five individuals belonging to each of the groups defined by wood density (WD) (low deciduous WD and high deciduous WD) were considered. In these plants, water potential measurements (Ψw), leaf area index and stomatal conductance (gs) were performed monthly, in addition to phenological observations of the species. Discrete humidity measurements were obtained monthly through two access tubes and through a capacitive Diviner probe. The experimental area has a flow tower that provided data on meteorological factors, such as rain, evapotranspiration, vapor pressure deficit, air temperature and humidity. The data were analyzed using the R software, in which Pearson correlations and means were compared by the Tukey test at 5% significance. It was found that the species evaluated responded to environmental factors in different ways and phenology is a reflection of the species' physiology and may undergo changes in response to water availability in the soil. The low WD species (C. leptophloeos) showed low Js, maintaining high Ψw and high gs, especially in the rainy season. The high WD species (C. pyramidale), on the other hand, maintained high rates of Js throughout the year, presented a very negative Ψw, probably to maintain the scarcest water intake from the soil. It is concluded that the seasonality of the rain acts in different ways in the hydraulic functioning of the species of the Caatinga, which present different strategies in response to drought and the species of high WD may have traits that favor greater acquisitions of resources, being these strategies, an evidence of greater survival of this functional group in future scenarios.