We subjected seedlings from three tree species from the semi-arid ''Caatinga'' biome to water deficiency and rehydration. The species were Bauhinia monandra K. and Hymenaea courbaril L., (both Fabaceae), and Tabebuia aurea (Bignoniaceae). Seedlings were kept under water restriction until photosynthesis decreased to values around zero. Plants were rehydrated and photosynthesis measured until its values reached values of well-watered plants. We measured leaf water potential, maximum quantum yield, and chlorophyll index on (1) the first day of the experiment; (2) when photosynthesis decreased to around zero; and (3) after photosynthesis recovery. We then determined biomass and leaf area. To avoid water deficiency B. monandra and T. aurea (but not H. courbaril) reduced their leaf area resulting in lower biomass accumulation. The chlorophyll index was also not affected in H. courbaril, but it was lower for the other two species under stress. Maximum quantum yield was equally decreased in all the tree species as a mechanism to decrease light damage of photosynthetic apparatus. Drought differentially affected the vegetative growths of B. monandra, T. aurea, and H. courbaril when time and intensity were considered, affecting leaf area status leading to the leaf biomass decrease. Decreases in soil moisture led to decreased gas exchange. However, leaves were positively acclimated using chlorophyll strategies by lowering the light harvest in photosystems, which protect photosynthetic reaction centers.

Water deficiency is a major abiotic stress that limits biomass production and drives plant species distributions. We evaluate the effects of water deficiency on ecophysiological and biochemical parameters of seedlings of Tabebuia aurea. Plants were subjected to daily watering (control) and to stress by soil water deficiency for 29 days. Leaf area, plant biomass, gas exchange, SPAD index, maximum quantum yield (Fv / Fm), quantum yield of PSII (ΦPSII), superoxide dismutase (SOD) and L-ascorbate peroxidase (APX) activity, lipid peroxidation, and proline content were recorded. Plants responded to water deficit by reducing leaf area and accumulating proline. Stomatal conductance was reduced to limit the water loss by transpiration. However, limiting CO2 uptake caused reduction in photosynthesis and biomass. The excess of energy unutilized by photosynthesis reduced SPAD index and ΦPSII. As a result, we observed an increase in SOD and APX activity, protecting chloroplast membranes from further damages caused by lipid peroxidation. Our results indicate that T. aurea have capacity to survive under water deficiency reducing stomatal aperture, but affecting the rate of CO2 assimilation. Nevertheless, plants showed mechanisms to preventing damages to the photosynthetic apparatus. Such plasticity is an important adaptation for plants growing in dry environmental.

Environmental filtering has been defined as the effect of environmental gradients on species in a plant community and can be the dominant driver of community assembly. Here, we evaluate the relationship between plant communities and the environment in the Restinga vegetation. For this, we measured 11 functional traits of plant species present along transects covering a marked edaphic environmental gradient. This gradient was characterized through Principal Component Analysis of soil characteristics. The relationships between the edaphic gradient and functional traits were evaluated using linear models. Finally, we compared the contributions of species turnover and intraspecific variation to among-site variation in functional traits. The gradients associated with soil nutrients (PCA axis 1) and soil acidity and organic matter (PCA axis 2) were then used to test the observed changes in community composition and were significant predictors of the distribution of water potential, leaf dry matter content and K content, height and chlorophyll index. Decomposing the total variation in the distribution of functional traits between species turnover and intraspecific variation revealed that species turnover explains a greater proportion of the observed variation. We conclude that community assembly is strongly limited by environmental filters and mediated by functional traits at the species level.