Climate change-induced drought has already contributed to increased plant mortality around the globe, including in forest ecosystems. Drought events are projected to become even more frequent in forests in the future and so, research into the drought responses of woody plants is an area of growing importance. Plants have two important attributes that regulate water balance: closable pores on the surface of the leaves (stomata) and long-distance water transport channels from the roots to the leaves (xylem conduits). Yet, how mortality and growth of tree species are influenced by stomatal control and xylem vulnerability to cavitation (air filling the normally water-filled vessels) is still being debated.
In a recent study published in AoBP, Chen et al. investigated the different responses of three understory tree species to drought. This study aimed to explore how future climate change caused droughts might affect vegetation succession in the region. The authors used a partial rainfall exclusion experiment to prevent precipitation reaching the soil. It was found that the synergistic effect of stomatal adjustment and xylem anti-cavitation ability was the key to drought resistance in plants of these ecosystems. Of the three species studied, two did not exhibit drought-induced dieback. Sorbus alnifolia did not close its stomata but had strong resistance to xylem cavitation under drought, whilst Dendrobenthamia japonica whilst highly vulnerable to cavitation, closed its stomata quickly in response to drought. The third species studied, Lindera obtusiloba, displayed hydraulic failure as a result of vulnerable xylem and an inability to close its stomata, with dieback occurring as a result. The authors conclude that by investigating the stomatal and xylem safety margins of understory forest species, we can interpret their sensitivity to drought and assess whether they will be successful under climate change scenarios.