Padrões morfoanatômicos e nutricionais de duas espécies (Vochysiaceae) acumuladoras de alumínio em savanas rochosas

Abstract

The water and nutrients are determining factors in the development of woody species in Neotropical savannas. In rocky Cerrado environments, soils are shallow and usually derived from highly weathered rocks, such as sandstone, resulting in high acidity, low nutrient availability, high aluminum (Al) saturation, and soil water deficit. The extreme conditions of rocky savannas require morphoanatomical adaptations to conserve water and nutrient resources, resulting in species exhibiting xeromorphic traits. In addition, some species have evolved internal Al tolerance mechanisms to cope with high edaphic Al concentrations and are able to accumulate this metal in high concentrations in the leaves (>1000 mg kg-1). Uniquely, some rock savannas may also occur on soils over limestone outcrops, characterized by high nutrient availability and marked water deficit. From this, we sought to understand how contrasting soils, i.g. calcareous and sandy Neosols, modulate the phenotypic expression and nutrient and Al uptake of the Al-accumulator species Callisthene fasciculata Mart. and Qualea parviflora Mart. Therefore, we quantified anatomical features (e.g. epidermis, mesophyll, vascular tissues), Specific Leaf Area (SLA), Fluctuating Asymmetry (FA), and nutrient (macro and micro) and Al concentrations of both species in the two edaphic types. Using Scanning Electron Microscope (SEM) with energy dispersive X-ray spectroscopy (EDS), we also evaluated the deposition of Al and nutrients in the different leaf tissues. In this study, we show that the calcareous Neosol influences greater tissue investment of the traits that prevent water loss in the leaf, mainly regarding the epidermis, in both species. Evaluating the deposition patterns and Al concentration in the leaves, we found that this metal is accumulated mainly in the leaf lamina tissues, independently of the edaphic Al concentrations. The leaves of C. fasciculata showed higher foliar Al concentrations in calcareous Neosol, where Al saturation is lower, and the species Q. parviflora showed no differences in foliar Al concentrations among soil types. Furthermore, we found that FA is an ecological indicator that is not very sensitive to edaphic variation in the two species studied, while SLA may indicate different ecological strategies of C. fasciculata populations, in response to increased nutrient availability, so that, in calcareous Neosols, this species increases its photosynthetic capacity and, consequently, carbon assimilation and productivity. On the other hand, the variation in nutrient availability between calcareous and sandy Neosols did not reflect in changes in the SLA of Q. parviflora, indicating that this species presents a conservative strategy of water and nutrient resources in both edaphic types.