Relations between carbon balance and water status under water deficit cycles in a green stem tropical species

Stored non-structural carbohydrates (NSC) and the ability to perform photosynthesis through green stems are efficient strategies under water limiting conditions. The objective of this study was to investigate the response of Commiphora leptophloeos , a species with green stems, to recurrent drought cycles. Young plants were subjected to four treatments: control (CO), control + stem light exclusion (CE), water deficit (D), and water deficit + stem light exclusion (DE), with two drought cycles interspersed with rehydration. During the first cycle, the CE treatment produced 3x more leaves than D and DE, and increased plant height by 79% compared to D and 58% compared to DE. Stem water content decreased in the DE plants. Plants under water deficit exhibited reduced 82% (stomatal conductance) g s three days after water exclusion in the first cycle and 45% after nine days in the second cycle. The maximum PSII efficiency in leaves decreased by 29% in DE plants compared to CE. The NSC concentration decreased by 63% in the water-deficit treatments compared to the controls during the second cycle, but only the coarse roots showed a change in NSC concentration. During the first cycle, the soluble sugars/starch ratio was altered in the leaves and stems, particularly in plants under DE conditions, but remained stable in the roots. These results suggest that maintaining water status, controlling g s , and reducing the number of leaves are crucial strategies for survival under water deficit conditions for this species, as the NSC concentration in the whole plant strongly decreased. Furthermore, our findings indicate that the stability of NSC in the stem may play a protective role.