Light acclimation of leaf gas exchange in two Tunisian cork oak populations from contrasting environmental conditions

Abstract

Due to diverse environmental conditions, Mediterranean plant populations are exposed to a range of selective pressures that may lead to phenotypic plasticity and local adaptation. We examined the effect of light acclimation on photosynthetic capacity in two Quercus suber (L.) populations that are native to different ecological conditions. Low-light adapted seedlings from both populations were exposed to three light treatments: full sunlight (HL), medium light (ML, 43% sunlight) and low light (LL, 15% sunlight) for one month. Photosynthetic performance was monitored by measuring leaf gas exchange and chlorophyll fluorescence parameters. The light environment influences light-saturated carbon assimilation (A max) in the leaves of the population inhabiting the hot and dry region (from Gaafour). In contrast, there was no significant difference in A max between leaves grown in high light and low light from Feija (the population native to a cold and humid climate), which suggests an inability of the Feija population to adjust its photosynthesis to respond to higher irradiance. The inability of the Feija population to adjust its photosynthesis did not result from a light acclimation failure in terms of chlorophyll content and ratio compared with the Gaafour population. Instead, it seems to be the consequence of lower stomatal conductance in the Feija population at HL compared to Gaafour.