Respostas ecofisiológicas de plântulas de espécies lenhosas da caatinga sob diferentes intensidades de radiação

Abstract

In seasonally dry tropical forests (FTS) vegetation is under the influence of water stress due to the high intensity radiation, high temperatures and irregular rainfall. This setting affects the development of mechanisms and ecophysiological strategies in plant species to overcome such conditions. However, groups of species may respond differently to the environment, especially when exposed to areas with different lighting conditions, such as are observed in ecosystems to human disturbance, found in FTS. The objective of this work was to evaluate the performance ecophysiological species of woody seedlings of savanna region under semiarid climate of Brazil, due to different levels of shading (full sun, 30% and 70%). The experiment was conducted in Serra Talhada / PE, for both were used 11 species, three individuals for treatment, which were related to the shading levels 30 and 70% and full sun. To analyze the performance of the species used an infrared gas analyzer (IRGA) to evaluate the following parameters: CO2 assimilation (A), stomatal conductance (gs), internal CO2 concentration (Ci), sweating (E), and the chlorophyll fluorescence. The leaf water potential (Ψf) and specific leaf area (SLA) were determined. All measurements were made at the end of the experiment. The efficiency of water use (USA) was determined by the A / E and instantaneous carboxylation efficiency (EiC) by the A / C. The results showed that groups of species studied varied little across the different light conditions, and for some parameters were no differences between species. The species had low water potential values, showed a decrease in gs, A, E and EiC. In fact observed Bauhinia cheilantha, wherein the water potential was 23% lower in the higher light intensity with a decrease in the gas by 36%, and 68% in photosynthesis. The kind that stood out was Comminphora leptophloeos that showed higher values of water potential and gas exchange in all light conditions. It was also noted that more negative water potential species exhibited higher AFEs as seen in Cynopholla flexuosa, in the shaded treatment, which had low water potential reflecting an increase of 20% in the AFE and the photochemical quenching coefficient (qP). While the parameters of IEF and chlorophyll have varied somewhat among light levels, trend was noted of higher chlorophyll content in ERA and most shading for all functional groups. The species showed small differences in water potential in different conditions, possibly due to irrigation controlled between light treatments. However, the groups of species of low wood density showed the highest values. Regarding other parameters, it was noted that the very negative water potential, reflected in lower gs, A, E and EiC. The highest intensity of radiation in some species such as L. rigida, reflected in a decrease in C, possibly due to partial stomatal closure and less qP, which caused decline in CO2 assimilation.