Leaf gas exchange variation under summer drought in Tunisian cork oak from geographically central and marginal populations

A global understanding of the ability of cork oak populations to cope with and adapt to summer drought stress is crucial for assessments of the future of cork oak forests as a major ecosystem in the Mediterranean. We examined the effect of summer drought on photosynthetic capacity in three Quercus suber (L.) populations that are native to different ecological conditions. Djebal Chahid (JCH) and Kef Errand (KER) originated from the driest sites and Feija (FEJ) from the wettest site. FEJ is the central area; however, JCH and KER are from geographically marginal sites of the species distribution range in Tunisia. The photosynthetic performance was monitored by measuring the leaf gas exchange and chlorophyll fluorescence parameters. The FEJ population leaves showed the lowest light-saturated rates of assimilation (Amax). However, the photosynthetic response curves as a function of photon flux density for leaves of different populations showed that the light compensation point was higher in FEJ compared to KER and JCH. The apparent quantum yield (Φ) was not significantly different between all the studied populations. The specific leaf area and chlorophyll content were similar in leaves of the studied populations, whilst assimilation seemed to be limited by stomatal factors. Our finding confirms previous studies showing a large population-level differentiation in cork oak with population from dry sites exhibiting a higher tolerance. This is useful to the forestry decision-makers to develop appropriate strategies to restore and protect forest ecosystems.