The extra-vascular water pathway regulates dynamic leaf hydraulic decline and recovery in Populus nigra

Leaf hydraulic conductance (Kleaf) is highly dynamic and typically responds to changes in water status and irradiance. However, the relative contribution of vascular (Kx) and extra-vascular (Kox) water pathways to Kleaf changes in response to water potential decline and recovery in function of light conditions remains poorly investigated. We investigated the dynamic responses of leaf hydraulics in Populus nigra L. by measuring Kleaf, Kx, and Kox changes under drought and upon recovery. Measurements were done at both low and high irradiance (LI and HI, respectively). Kleaf increased and became more vulnerable to dehydration under HI conditions than LI, due to marked changes of Kox. After re-watering, Kleaf recovered in parallel with Kox recovery, but Kleaf response to irradiance remained inhibited. Strong correlations between Kleaf and drought-induced membrane damage demonstrated the relevance of the cell-to-cell water pathway in driving the dynamic responses of Kleaf under drought and recovery. Our findings highlight the importance of coordination between water and light availability in modulating the overall Kleaf response to environmental conditions.