Drought-stress tolerance in three semi-arid species used to recover logged areas

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.