IMPLICAÇÕES ECOFISIOLÓGICAS DAS VARIAÇÕES ESTRUTURAIS E FUNCIONAIS DE COMPONENTES DA CASCA EM ESPÉCIES DO CERRADO: UMA ESTRUTURA MOLDADA PELO FOGO, MAS TAMBÉM PELA ÁGUA

Abstract

The climate of the Cerrado is characterized by a long period of drought and the occurrence of fires is frequent. This combination of fire and water restriction was possibly a determining factor in the emergence of the large numbers of plant species, which contrasted significantly in their relative investments in wood and hulls. However, it is important to highlight that, to date, a good part of the studies related to the hulls in Cerrado plants had as its main focus only the adjustments induced by fire. Thus, little is known about what impacts the structural variations of the hulls can cause on other ecological aspects, such as water transport and carbon assimilation, especially among species with different growth strategies present in this biome. In this sense, the main objective of this work was to analyze how the variations in the structural and functional properties of the hulls are related to central physiological processes among different species of the Cerrado. For this, 31 native species, widely distributed in the Cerrado, were analyzed for the following parameters: morphological analysis (total hulls thickness, internal and external hulls thickness, stem diameter, hulls and wood density, braches growth rate); water relations (water content in leaves, wood and hulls, percentage of water in the stem stored by the hulls, leaf and stem water potential, stem capacitance, stem hydraulic conductivity); and carbon fixation (net carbon assimilation). xvi After the analysis of the morphological and physiological traits, the experimental area suffered the incidence of a large burn, which allowed observing the survival rate of the species after the fire. In general, the remarkable fire tolerance of the plants from Cerrado could be clearly observed in the present study, since no individual of the 31 species studied died after the occurrence of burning. By all indications, this ability to tolerate fire was directly related to structural aspects of the hulls, more specifically thickness. Our results also confirm the hypothesis that the structural variations of the bark in Cerrado plants, besides being a response to the selective pressure exerted by the fire, possibly involves the participation of this structure in the regulation of the water status, as well as the fixation and transport of carbohydrates. In addition, we have also demonstrated that different hulls structures may assume contrasting ecological functions, with the outer portion being more directly associated with fire protection, while the inner portion was more strongly related to water status regulation and transport of carbohydrates. Thus, the present work significantly increases the knowledge about the Ecophysiology of plants from one of the largest and most diverse Brazilian biomes.