Drought tolerance mechanisms of a woody evergreen in a tropical dry forest

In tropical dry forests (TDF), most woody species tolerate annual drought periods via a deciduous life history strategy. However, TDF also present evergreen trees, which are supposed to develop different traits to tolerate the dry season. Herein, we investigated the physiological traits in the leaf, stem, and root of the evergreen shrub Cynophalla flexuosa. In these three organs, we measured non-structural carbohydrate (NSC) concentration, and nitrogen (N), phosphorus (P), and potassium (K) concentration. The traits xylem water potential (ð) and stomatal conductance (gs) was also measured. We reported high stability of gs throughout the seasons, despite high variation in soil moisture and vapor pressure deficit. The leaf morphoanatomy such as hypostomatic distribution and the papillose groove structure above stomata might be supporting that response. In all seasons, Yx declined every morning but was fully recovered by the evening. Storage and redistribution of NSC and N, P, and K among tissues appeared to be regulated more by C. flexuosa phenophases than by environmental water availability. During the dry season, the plants presented resprouting leaves, high NSC concentration in the leaf and root, and high N concentration in the leaf and stem. These results suggest that high NSC root concentrations is crucial for maintaining high water uptake efficiency during all seasons. Our results suggest that drought tolerance of the woody evergreen C. flexuosa in a tropical dry forest is achieved via mobilization of non-structural carbohydrates and nutrients and rapid daily recovery of water status.