Partição da evapotranspiração em uma floresta de terra firme na Amazônia Central

Abstract

The Amazon Forest is the largest tropical forest in the world, having an important relevance for its immense biodiversity and for its regulatory role in the global climate system. With emphasis on the mechanisms of recycling of precipitation in which the transfer of water by evapotranspiration (ET) is important, and maintained by the stock of water in the soil, which sustains the ecosystem of the tropical forest during the dry season. Faced with climate change scenarios, understanding the partition of ET into its constituent components (evaporation (E) and transpiration (T)) and its relationship with the dynamics of water in the soil and the mechanisms of water use by vegetation is a major challenge. Especially when considering the diverse composition of forest trees that are conditioned and respond differently to changes in water in the soil. The present study was carried out in a plateau area located in a mature forest in Central Amazonia, where the contribution of soil water content and three groups of trees to evapotranspiration was evaluated. The soil water content in the deep layers proved to be an important water reserve to maintain ET in the dry period, and in prolonged periods without precipitation in the rainy season. It was verified the occurrence of a mechanism of water extraction by the roots, which access the deep layers as the availability of water in the superficial layers decreases. It was observed that water extractions can reach up to 8.80 meters deep in the soil. Another factor observed is that the vertical variation of the water content in the soil is influenced by the physical characteristics of the soil that favor the formation of preferential zones of water extraction. The TE partition during the analyzed period showed that 35% (476 mm) of precipitation (1409 mm) returned to the atmosphere in the TE process, with 13% (61 mm) being intercepted, while sweating contributed 87% (415 mm) ). The greatest contribution to perspiration losses came from trees emerging from the canopy, with 49% (203 mm), followed by subdossel and understory trees, with 31% (128 mm) and 20% (84 mm), respectively. In addition, sap flow analysis revealed specific T patterns for tree classes. Variations in the amplitude of T show that although emerging trees dominate T losses, other trees play an important role in ET, especially during the dry season, when the reduction of T losses by emerging trees occurs. This reduction was offset by the increase in T in the sub-crown and understory trees. These results show the importance of systematic and continuous observations for the evaluation of the ET partition in different strata of the Amazonian forest and for the understanding of the ecosystem's resilience to potential changes in the hydrological regime associated with variability and climate changes.