Fluxo de Seiva e Crescimento de Árvores em Função das Variáveis Climáticas em Espécies Arbóreas na Amazônia Central

Abstract

The Amazon contains a large area of tropical forest and has been intensively studied regarding its role of global climate. However, deforestation and climate change are affecting the hydrological cycle in the Amazon. The objectives of this study were to: (i) determine which are the most important climate variables that affect the monthly increase in growth and the sap flow of trees; (ii) determine if the monthly increment in growth and the sap flow of the trees are affected by seasonality; (iii) determine how interspecific variations affect the increase in diameter and the sap flow of the study species. The study area was conducted is a primary terra firme rainforest in the Reserva ZF2. The climate parameters were measured at the top of an observation tower (C14 of the ZF2 Reserve) 40 meters in height. In the study, the monthly increment in diameter (IMD) was obtained from monthly measurements of trunk diameter in 56 trees from ten species, with diameter at breath height above 15 cm, during 2013 to 2016. The water flow in the trunk of the trees was measured with sap flow meters (SFM1, ICT, Australia) using the heat ratio method (HRM Heat Ratio Method) in 46 adult trees, distributed in 10 species. The mean annual precipitation (2013-2016) of the area was 2226.1 mm. It was observed the El Niño climate phenomenon between the years of 2015 and 2016, which influenced the pattern of rainfall distribution, causing a reduction of the incident rainfall. Thus, in 2015 the lowest annual rainfall (1842.9 mm) was recorded. The mean (of 48 months) water content in the soil was 44% (v/v). In the dry season of 2015 it was recored the lowest value of 32% (v/v) in October 2015, and the maximum value of 51% (v/v) was recorded in March 2015. The mean temperature was 26 °C, and the maximum was 36 °C (September 2015), which occurred at noon. Relative humidity was on average 79.5% ranging from 30% at noon (September 2015) to 99.9% during the nighttime period over the sudy period. The general monthly mean photosynthetically active radiation (RFA) was 27.7 mol m-2 d-1, the mean monthly IMD was 0.181±0.094 mm, and the annual mean IMD was 2.119±0.262 mm. There was variation in IMD between months in the ten species. IMD was higher in T. venusta (0.528 mm), followed by the species L. micrantha and S. micranthum (0.273 and 0.226 mm), whereas E. collina, G. argenteum showed the lowest IMD with 0.056 and 0.093 mm per month, respectively. The climate variables rain and RHmin had a positive effect on IMD variation. Whereas, maximum temperature (Tmax), RHmax and soil moisture had a negative effect on IMD variation. Wood density (DM) influenced the IMD, less dense woods showed greater variations xi in IMD (T. venusta). Taller trees had higher IMD. The sap flow ranged from 1.5 L h-1 (in I. laurine) to 12 L h-1 recorded in S. micranthum, and the lowest and highest sap flow volumes were 22.1 L d-1 (in I. laurina) and 145.4 L d-1 recorded in S. micranthum. Variations of the maximum sap flow velocities were 11.4 cm h-1 (I. laurina) and 41.2 cm h-1 recorded in P. decandrum. Parameters of the physical enviroment that most affected the sap flow rates were rain, minimum temperature (Tmin), RHmin, and soil water content. There was a close relationship between sap velocity and DPV and RFA. There was an inverse relationship betwee wood density (DM) and sap velocity. There was a relationship between the size of the trees in sap flow and in the IMD. Thus, the sap flows were larger in trees with greater DBH and height (P <0,001). This study shows the importance of factors of the physical environment on sap flow of trees, and their relationship with the variation in diameter of trees, as well as the variations in the performance of trees associated with interspecific differences.