Dynamic changes of leaf hydraulic conductance in response to dehydratation and re-watering under low vs high irradiance

Leaf hydraulic conductance (KL) is higly dynamic and typically responds to water status and irradiance. However, the relative contribution of vascular (Kx) and extra-vascular (Kox) leaf water pathways to KL changes in response to water potential decline and recovery, as a function of light conditions, remains poorly investigated. We studied dynamic responses of leaf hydraulics in an evergreen (Arbutus unedo L.) and a deciduous (Populus nigra L.) tree species. We estimated the vulnerability of KL, Kx and Kox during dehydration, and the eventual recovery after re-watering leaves that experienced turgor loss. Measurements were performed at both low and high irradiance, and by using the vacuum chamber method (VCM) and the evaporative flux method (EFM). KL vulnerability was higher under high irradiance, as a result of marked changes in Kox. Moreover, KL recovery, as recorded in response to re-watering, was mostly due to Kox recovery in both species.