Estratégias de segurança hidráulica e características anatômicas de plantas lenhosas da Caatinga em resposta à sazonalidade climática

Abstract

Seasonally dry tropical forest plants are susceptible to the cavitation of their pots, both in leaves and in the wood, having a greater tension in the water column and managing a trade-off between efficiency and hydraulic safety, which is reflected in the density of wood and structure of the xylem. However, the interrelationship between biological and hydraulic parameters is complex and little explored, and this correlation is essential for the best compression of drought tolerance. The objective of this work was to test the hypothesis that plants in the semiarid region have different mechanisms and tolerance to drought as a function of wood density. The anatomical, phenological and physiological characteristics of four woody species from the caatinga were analyzed, belonging to two groups, two with high wood density (HWD) and two with low wood density (LWD). The study was carried out in a caatinga area, semiarid region of Brazil, where monthly data were collected, for one year, on phenology, xylem water potential and stomatal conductance. In addition, the leaves and branches were performed to analyze the anatomical structure. The R software was used on the RStudio v 1.1.46 - 2009-2018 and SigmaPlot version 14 platform, for statistical analysis and graphics production. As expected, the density of the wood along with the phenology, anatomy and physiology was crucial to understand the goals of efficiency and hydraulic safety. LWD species class a preventive strategy, while HWD species were more tolerant to drought. As a preventive way, as BDM species lost as leaves before starting the dry season, potential hydraulic conductivity dissipation 66.78% higher than HWD species, as well as higher stomatal density (24.81%). However, LWD species were 54.18% more vulnerable to hydraulic failures than HWD species. The HWD species anatomically more resistant leaves, with the presence of gelatinous fibers next to a sclerenchyma sheath specific to a central rib, not being observed in LWD species. These data indicate that HWD species have a greater tolerance to drought because they have a more resistant hydraulic architecture. On the other hand, as LWD species use preventive strategies, maintaining their high water potential to prevent the collapse of the hydraulic system during the dry period. Based on the results, an interrelation of biological and hydraulic factors determines the plant's drought performance as a function of the functional group, demonstrating that adaptive groups may differ depending on the drought