Water relations of Caatinga trees in the dry season

The Caatinga is one of the world's richest dry forests. This forest occurs only in Brazil, but is the least studied and protected Brazilian ecosystem. There are few reports about drought tolerance mechanisms in Caatinga trees. This work evaluates water relations of six adult species in the middle of the dry season to further understand water relations in this ecosystem, which will be important for future reforestation and management projects. Based on results, the trees were classified into four groups: (I), Mimosa caesalpiniifolia had low leaf water potential (Ψw) at predawn and no significant decrease at midday. Stomatal conductance (gs) analyses indicates that plants have reached its lowest Ψw; (II), Caesalpinia pyramidalis and Auxemma oncocalyx had low Ψw at predawn and significant decrease at midday. For these species the recuperation of water status at night may have been sufficient for maintaining stomata open during the day; (III), Caesalpinia ferrea and Calliandra spinosa had relatively high Ψw at predawn and a significant decrease at midday. These species might maintain their water status similar to individuals of group II, but they might also have deeper root systems; and (IV), Tabebuia caraiba with the highest Ψw at predawn and no significant decrease at midday, possibly indicating a combination of good stomatal control of water loss and a deeper root system. Moreover, except for individuals of group I, both in species with lower and higher Ψw at predawn it was not observed strong inhibition of gs.

Research Highlights
► Caatinga trees submitted to water shortage.
► Different responses in water potential and stomatal conductance.
► Differential resistance mechanisms.