Vulnerability segmentation between proximal and distal organs – between the leaves, which are more vulnerable, to drought-induced cavitation, and the terminal stems – is known to act as a “safety valve” to protect hydraulic pathways from dysfunction. However, it requires further studies to determine whether vulnerability segmentation maintains the hydraulic safety of tree species differing in leaf phenology in arid ecosystems.
Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) investigated leaf and stem hydraulic properties as well as seasonal variations in water potential and stomatal conductance in three sympatrictree species of Anacardiaceae（evergreen Pistacia weinmanniifolia, drought-deciduous Terminthia paniculata, and winter-deciduous Lannea coromandelica）in a Chinese savanna. They aimed to identify the potential divergent strategies that maintain the hydraulic safety of the whole plant, and also to identify the hydraulic-related structural traits responsible forinter-species differences in hydraulic safety.
Vulnerability segmentation was found in the evergreen P. weinmanniifolia and the winter-deciduous L. coromandelica. By sacrificing the cheaper and more vulnerable leaves, the winter-deciduous species showed a drought-avoidance strategythat maintained the hydraulic safety of the more carbon-costly stems. The evergreen species showed a hydraulic strategy of drought tolerance with strong stomatal regulation.
In contrast, the drought-deciduous T. paniculata lacked vulnerability segmentation and shed leaves at the cost of some top shoots during peak drought. In addition, the differences in leaf and stem hydraulic architecture among these species are closely related to their structural traits.
The results implied that even sympatric tree species can exhibit divergent adaptive hydraulic safety strategies. The hydraulic properties of the three tree species have co-evolved with their structural traits.