Diversidade anatômica e hidráulica em espécies lenhosas de savanas neotropicais

Abstract

Neotropical savannas have a high diversity of species distributed in a mosaic of phytophysiognomies that include field vegetation, savannas, forests, and a climate with significant seasonality in precipitation. The increase in the frequency of drought events in recent decades has caused instability in species dynamics and distribution. The factors related to the climate, water content, nutrients in the soil, topography, and disturbances like fire act synergistically, determining the limits of these physiognomies. These conditions possibly act as environmental filters for the species, defining the community limits and functioning under different resource levels. Compared to forest ecossystems, savanna physiognomies naturally occur in environments with less precipitation and, consequently, less water availability in the soil and high vapor pressure in the atmosphere, boosting the functioning to withstand high levels of atmospheric and edaphic drought. Therefore, determinants of the species permanence in savannas may be linked to the species' hydraulic functioning. This capacity can be linked to coordinated ecological strategies among all the plant organs, which in savanna environments can be highly diverse, diverging, or converging between the species that make up the communities. This work aimed to evaluate twenty-eight species hydraulic functioning covering 60% of the domain of three neotropical savannas (Amazonian savanna, typical cerrado, and cerrado rupestre), with different levels of precipitation and topography, using an integrated approach of morphological attributes, anatomical and hydraulic. The correlations between the structural attributes of the leaf and the wood with the hydraulic resistance were investigated. Embolism resistance (P50) and hydraulic safety margin of embolism resistance in xylem and carbon isotope were considered predictors of a proxy for water use efficiency. This study provides new insights into the different strategies that plants can develop in an integrated manner and represents the first work that compares the hydraulic architecture of species in an Amazonian savannah with savannas in the central plateau. The results show that species that live in restricted environments can present different forms of drought tolerance, with different ecological strategies. These different species strategies suggest similar consequences for maintaining a favorable water balance. With future predictions about drought events, studies that increase the understanding of savanna species' hydraulic functioning can be good predictors of the impacts of extreme events on the community and, consequently, on the ecosystem functioning.