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

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

Automated summary

The study found that leaf hydraulic conductance increased and became more vulnerable to dehydration under high irradiance conditions, mainly due to marked changes in the extra-vascular water pathway. After re-watering, leaf hydraulic conductance recovered in parallel with extra-vascular recovery, but its response to irradiance remained inhibited.