Aclimatação a redução do volume de solo molhado e fluxo de seiva no guaranazeiro

Abstract

Brazil is the only commercial producer of guarana (Paullinia cupana) in the world. The crop is traditionally exploited in humid environments in the North, Northeast and Midwest regions, without the use of irrigation. In the scientific literature don’t exist works about the dynamics of water in the guarana tree, information that is extremely important for correct planning and management of irrigation. The objective of this work was to study the dynamics of water in guarana, in order to understand the mechanisms of acclimatization of the culture exposed to water deficit and reduction of the volume of wet soil. For this purpose, two experimental areas were implemented, the first in a protected environment with young guarana plants in 500 L pots and the second with adult plants in a producing property. The first chapter discusses the uncertainties related to the estimate of sap flow by the Granier method and transpiration obtained with a weighing lysimeter and establishes the relationships between the water demand of the atmosphere with the sap flow and the leaf area of the guarana tree in the productive stage. In the second chapter, the acclimatization of young guarana plants to the reduction in the volume of wet soil was studied. The sap flow relative to the control treatment was observed over time and in relation to the reference evapotranspiration (ETo) of the period, the variation in leaf area, root density and the difference in leaf temperature between treatments. The third chapter proposes the use of punctual leaf temperature measurements in a leaf energy balance method to estimate guarana transpiration under full and deficit irrigation conditions. Sap flow was used to estimate the absorptivity of solar radiation from the leaf, a variable used in the energy balance. It can be concluded that the volume of wet soil has a great influence on the water dynamics for the crop, requiring care in localized irrigation during dry spells in humid regions. The leaf temperature associated with the leaf energy balance method allows estimating transpiration even with discontinuous measurements. The relationship between leaf area, sap flow and ETo varied with plant development and there are differences in transpiration processes and sap flow in daily temporal scales, which can influence the efficiency of irrigation management since irrigation aims to restore the water taken from the soil, which may not correspond to evapotranspirated water in this interval.