Anatomy and eco-physiology of leaves and twigs of Cistus incanus L.: adaptive strategies to the environmental constraints of the Mediterranean ecosystems.

Plants of Mediterranean-type ecosystems are exposed to climatic conditions that may limit carbon metabolism resulting in limitation of productivity and growth. During springtime, photosynthetic activity and plant growth are promoted, while they are constrained by aridity in summer and by low temperatures in winter. To overcome such stressful conditions, Mediterranean species have developed strategies expressed by phenological, physiological and structural modifications. Among the various woody species of the Mediterranean maquis in Southern Italy, Cistus incanus L. shows its phenology and cambial activity strictly related to the annual fluctuations of the environmental conditions. In this study, several structural, functional and eco-physiological characteristics were investigated on plants of C. incanus sampled during the autumn development in the Castevolturno Nature Reserve (NA, Italy). Anatomical and cytological features of leaves and twigs were analysed through light and fluorescence microscopy, mainly focusing on traits associated to a) regulation of water relations and b) protection of tissues from excessive irradiation and permanent injuries due to drought and predation. Efficiency and safety of the vascular system were evaluated on the basis of a detailed analysis of the xylem cell types. As regards eco-physiological behaviour, simultaneous measurements of gas exchange and chlorophyll fluorescence were conducted on fully expanded leaves at midday under saturating light intensity. The following parameters were analyzed: net photosynthesis (PN), stomatal conductance (gtH2O), water use efficiency (A/E) and quantum yield of PSII electron transport (Fe). All data were interpreted under ecological and functional perspectives.