Do woody plants of the Caatinga show a higher degree of xeromorphism than in the Cerrado?

The maintenance and success of plants in different environments is tied to water availability, to the capacities in water transport and to the development of strategies to deal with water deficit. Here, we conducted a study in two seasonally dry Brazilian phytogeographic domains: the Cerrado and the Caatinga to evaluate whether the adaptive wood anatomy strategies to deal with water deficit would be the same for two species that occur in both domains, and which variables would best explain the variation in wood anatomy variables. Qualitative and quantitative wood anatomy, Student's t-tests, permutational multivariate analyses of variance (PERMANOVA) and pair-contrast analyses were done for 20 specimens of Tabebuia aurea and Tocoyena formosa from both environments. Our results showed that species was the strongest variable to explain the variation in the data. But, the environment also appeared as an important variable. Even the Caatinga being drier than the Cerrado, this did not result in a higher degree of xeromorphism for both species in the Caatinga. Each species, in each environment showed different strategies to deal with water availability: while vessel diameter and intervessel pit morphology indicate a higher xeromorphic degree for T. aurea from the Caatinga, vessel grouping index, vessel density, and vessel-ray pit morphology indicate a higher xeromorphic degree of T. formosa from the Cerrado. We suggest that the oligotrophic soil and the presence of aluminum in soil may influence the degree of xeromorphism in wood anatomy structure.