Mecanismos hidráulicos de tolerância à seca de bertholletia excelsa bonpl.

Abstract

Bertholletia excelsa is a large tree species widely distributed in the Amazon with social and economic importance. The tree species water regulation and tolerance responses to extreme drought events, such as El Niño, are currently missing. There is no information on the impacts of severe droughts on the physiology of this species. Thus, the present study aims to identify the drought resistance mechanisms of Bertholletia excelsa. Thus, the present study aims to investigate the drought resistance mechanisms of Bertholletia excelsa. The study was performed at Aruanã farm (Itacoatiara-AM), considering nine trees with leaves of different ages (young, mature, and old). We build embolism vulnerability curves to estimate the points of 12%, 50%, and 88% of loss of hydraulic conductivity (P12, P50, and P88, respectively). Leaf drought tolerance was also studied through pressure-volume curves and estimated water potential at maximum turgor (Po), water potential at the turgor loss point (PPT), modulus of elasticity (E) and saturated water content (CRSA). The water regulation responses of Bertholletia excelsa represent hydraulic systems with intermediate resistance to embolism (average P50 = -2.58 MPa). However, this was associated with the loss in the water regulation capacity of the leaves as they are aging, reflecting a reduction in the hydraulic safety margin (HSM) in the dry season - HSM = 0.46 MPa; HSM is the difference between the P50 and the minimum water potential measured in the field. The leaf phenology is coordinated with the water regulation physiology. The young and mature leaves adjust their water potential through structural adjustments to maintain their water content. At the same time, old leaf shedding acts to reduce water loss through transpiration during the dry season, resulting in a complementary mechanism that likely helps the plant survive during the seasonal dry period. Because old leaves develop limited control of water status, as confirmed by field-measured water potential and water content in mature-old leaves. In conclusion, Bertholletia excelsa species seems to be adapted to seasonal droughts. However, with increasing frequency and intensity of droughts, the species may face problems adapting the coordinated responses between leaf, xylem, and phenology, affecting the species growth, fruit production and leading to mortality from hydraulic failure under prolonged drought conditions. Furthermore, these accumulated effects can reduce the suitable areas where the species can occur in the Amazon, affecting the natural occurrence and potential plantations throughout the Amazon.