Within-crown variation in leaf conductance of Norway spruce: Effects of irradiance, vapour pressure deficit, leaf water status and plant hydraulic constraints

Abstract

Responses of leaf conductance (gL) to variation in photosynthetic photon flux density, leaf-to-air vapour pressure difference, shoot water potential and soil-to-leaf hydraulic conductance (GT) were studied in Picea abies (L.) Karst. foliage with respect to shoot age and position within the canopy. The upper canopy shoots demonstrated on average 1.6 times higher daily maximum gL as compared to the lower canopy shoots growing in the shadow of upper branches. Functional acclimation of the shade foliage occurred in the form of both a steeper initial slope of the light-response curve and a lower light-saturation point of gL. The mean GT was 1.6-1.8 times bigger for the upper canopy compared to the lower canopy. We set up an hypothesis that stomatal conductance at the base of the live crown is constrained not only by low light availability but also by plant's inner hydraulic limitations.