FLUXO DE SEIVA E TRANSPIRAÇÃO DE PLANTAS JOVENS DE MOGNO BRASILEIRO (Swietenia macrophylla King) SOB REGIME VARIÁVEL DE ÁGUA NO SOLO

Abstract

Brazilian mahogany (Swietenia macrophylla King) is a forest species of economic and environmental interest due to its wood’s great finish and its use in recovering and recomposing ecosystems. However, clarification on how this species uses water resources is still necessary. Therefore, in chapter one, the objective was to evaluate sap flow and transpiration behavior in young Brazilian mahogany plants under variable conditions of soil water potential. The study was carried out in a protected environment and cultivated the plants in weighing lysimeters wherein the soil underwent potential variations between -10 kPa and -35 kPa during water restriction, rehydration, and full irrigation periods. To quantify water use in mahogany plants, we measured sap flow through heat pulses, transpiration through the weighing lysimeters, and evapotranspiration rate by time variables. It was observed that sap flow and transpiration are affected negatively by soil water potential variation. The leaves lost water to the atmosphere under water deficit conditions, even with the absence of upward sap flow. Sap flow was restored four days after irrigation had resumed. In chapter two, the objective was to contribute with the uncertainties (U) involved in the heat ratio method application used to determine in the Brazilian mahogany sap flow. For this, sets of heating probes and temperature measurement were installed in plants of eighteen months of age, cultivated in Yellow Latosol, under weighing lysimeter and located in a protected environment. The uncertainty in the sap flow was calculated by the combination between the uncertainty in the thermal diffusivity (Uk), the conductive section (USc) and the corrected sap velocity (UVc). It was observed that Ik has greater weight in determining the sap flow of Brazilian mahogany, when compared to USc and UVc .It is necessary to adjust the thermal diffusivity during the cycle, or period evaluated, in order to improve the heat ratio method accuracy, because the sap flow overestimated the Brazilian mahogany transpiration in optimal soil water conditions by fifteen percent.