Seasonal balance of whole plant non-structural carbohydrates in a deciduous species with green stem in a dry tropical forest

Abstract

We investigated the dynamics of non-structural carbohydrates (NSC) in a deciduous species with a green stem, under semiarid seasonality. The predawn xylem water potential (Ψ_x) always remained high (≥−0.5 MPa). However, the NSC total concentration was reduced by approximately 75% when the plants were leafless. Stomatal conductance, leaf and stem photochemical activity, and mineral nutrition varied under the seasonality. Stomata had greater conductance when the soil water balance was positive. In the driest year, lower nutrient concentrations were found in the leaves, and higher concentrations were found in the stems than in the wettest year. Commiphora leptophloeos has a phenology that promotes leaf fall at the beginning of the dry season and regrowth of new leaves at the end of the dry season, following the photoperiod and not soil water availability. Due to deciduousness, the plants maintained a high Ψ_x, however, the green stem seems to have only contributed to maintaining the concentration of stored starch. Such behavior could increase the susceptibility of this species to prolonged drought season, as predicted for the semiarid regions. Thus, sprouting new leaves still during the dry season would deplete the NSC stock and increase water loss.