How leaf structure matches photosynthesis in different plant species of Mediterranean maquis ecosystem.

In Mediterranean regions plants are often exposed to several environmental factors that limit their growth and productivity. The high air temperatures and the low soil water supply due to the summer drought are known as the primary constraints in affecting plant photosynthetic performance. In this study, we have compared the functional leaf traits and the photosynthetic performance of sclerophyllous and semi-deciduous species widely spread in the Mediterranean maquis of southern Italy. The results show that the evergreen sclerophyllous species (e.g. Pistacia lentiscus L. Phillyrea angustifolia L., Quercus ilex L.) and semideciduous species (e.g. Cistus incanus L., Cistus salvifolius L.) modulated the photosynthetic activity differently during the summer season and showed leaf structural properties linked to intrinsic plant capability to overcome the stress. More specifically, the evergreen sclerophyllous species showed higher photosynthetic rates (AN) and water use efficiency (WUE) compared to semi-deciduous species and have leaves characterised by higher mass per unit leaf area (LMA) and tissue density (LTD) as well as lower relative water content (RWC) and thickness (L) compared to semi-deciduous species, which exhibited the lowest carbon/nitrogen ratio. The difference in functional leaf traits among species significantly affected the photosynthetic behaviour in terms of light absorption and plant carbon balance: the sclerophyllous evergreens utilize the absorbed light more in photochemical processes, as indicated by higher rate of quantum yield of PSII electron transport (FPSII) and electron transport rate (ETR); the semideciduous species prevent the photoinhibitory damage risks dissipating the excess of light energy by non-radiative dissipation process as shown by higher values of non-photochemical quenching (NPQ). The different photosynthetic regulation accomplished by changes in leaf structure guarantees the adaptive success of these species in their environment.