Response of the Mediterranean species Cistus salvifolius L. to the rise of winter temperatures: morphological and physiological adaptations

The rise of atmospheric CO2 concentration up to 600 ppm predicted in this century will drive a deep change in the future climate. The impact of these alterations will be particularly evident in the Mediterranean Basin where an higher frequency of extreme events such as drought and heat waves are expected. In this context, the survival of the Mediterranean species will depend on their capability to adapt to the new environmental conditions. Sclerophyllous species, and in particular the evergreens, seem to be susceptible to climatic change being slow in the adaptation to changing environmental conditions. In this work the response of Cistus salvifolius L. to the rise of winter temperature has been studied. This semi-deciduous species, widespread in Mediterranean areas, has been considered a suitable model for its high ability to adapt to Mediterranean climate. Plant acclimated to winter conditions (outdoor) were moved into a greenhouse (indoor) at higher temperature and eco-physiological behaviour was analyzed on leaves after 15 days from plant transferring (IND15d) and on new leaves developed indoor (IND). IND leaves were characterized by reduced thickness, higher specific leaf area (SLA), higher CO2 mesophyll conductance and photosynthetic rate than leaves grown outdoor (OUT) upon current winter conditions. In IND15d leaves no improvement of photochemical activity was found. When IND leaves were subjected to rapid increase of air temperature the CO2 fixation was not limited indicating an high thermotolerance of photosynthetic machinery. The results for IND leaves suggest the occurrence of a strategy that merging changes in leaf structure and photosynthetic regulation allows C. salvifolius to maintain an elevated carbon gain during both fast or slow increases of temperature.