Influência do microclima de uma floresta primária de baixio e de platô sobre a temperatura e trocas gasosa foliares de duas espécies árboreas na Amazônia central

Abstract

Understand the interactions of the continuous soil-plant-atmosphere are important to increase the knowledge about the forest ecosystems and their interactions with the climatic system. In this context, this work had the objective to investigate the influence of the variation of the topographical characteristics (valley and plateau) and of the microclimatic conditions on the leaf temperature and the gas exchange of leaves of two arboreal species of a pristine forest in the Amazonian Central. The research was carried in the Biological Reservation of Cuieiras (2º35`22 `` S, 60º06`55 `` W). The studied species were cardeiro (Scleronema micranthum) and matamata (Eschweilera sp. and Eschweilera aff. micrantha (Berg.) Miers.). The research was conduct at the year of 2007, during the time of lower precipitation in the area, being this time subdivided in three periods: the period I understood the months of June and July, that it comprehend to the beginning of the dry station, the period II the months of August and September, that it comprehend to the intermediate and final part of the dry station and the period III the months of October and November, that it comprehend to the final part of the dry station and beginning of the rainy station. The climatic variables were obtained from the instrumentation installed in two towers of climatic observation already existent at the site, being one at the valley and another one at the plateau. The other variables analyzed were: characteristics chemical, nutritional and texture of the soil; leaves nutrients, leaf area (LA), specific leaf area (SLA), water potential at the leaf ( w), leaf temperature, gas exchange and chlorophyll a fluorescence. The results show that the leaf temperature presented great variation in the two species studied at the plateau (it was impossible to determine Tf in the plants of the valley) during the period II and III, period that this variable was measured. Thus, it was verified that these variations were well correlated with the photosynthetic radiation, with the temperature of the air and with the relative humidity of the air. The leaf gas exchange showed outstanding difference between topographical categories, where the plants of the valley presented greatest photosynthetic taxes than the plateau plants. For the variables of the chlorophyll a fluorescence, the studied individuals exhibited good capacity to capture and use the solar energy in the biophysical processes, reducing the potential effect of the stress caused by photoinhibition. This way, regarding to the experiments time, period of smaller precipitation and the need of the trees to intensify the mechanisms of maintenance of leaf temperature, it is believed that the trees of the valley could accomplish this function with better performance, due to smaller height of the trees, larger phosphorus and potassium contend and larger concentration of atmospheric CO2 in the valley, presenting this way, larger taxes of leaf gas exchange than the plants of the plateau. Therefore, it was concluded that the leaf temperature and the leaf gas exchange are variable sensitive to register the effect of the different characteristics of the soils, associated to the topographical variations on the plantmicroclimate interactions at the canopy in the Amazonian forest.