Morphological and physiological modifications of Cistus salvifolius L. winter leaves in response to the rise in winter temperatures

The global climate is predicted to change in the next century; for the Mediterranean Basin, an increase in air temperature more than 4°C and a higher frequency of extreme climatic events such as drought and heat waves are expected. In this work, the response of Cistus salvifolius L. to the rise in winter temperature has been studied. Plants acclimated to winter conditions outdoor (OUT)] were moved into a greenhouse indoor (IND)] at higher temperature and eco-physiological behaviour was analysed on leaves after 15 days from plant transferring (IND_15d) and on leaves developed IND. IND leaves were characterized by reduced thickness, higher specific leaf area, higher CO₂ mesophyll conductance and photosynthetic rate, and lower respiratory rate than leaves grown OUT upon current winter conditions. In IND_15d leaves, no improvement of photochemical activity was found. When IND leaves were subjected to a rapid increase in air temperature, the CO₂ fixation was not limited indicating a high thermotolerance of photosynthetic machinery. The results for IND leaves indicate the occurrence of a strategy that merging changes in leaf structure as well as in photosynthetic regulation allow C. salvifolius to maintain an elevated carbon gain in response to temperature increase.