Physiological and morphological acclimation of Cistus salviflorus L. winter leaves to elevated temperatures

Plants of Mediterranean ecosystems rely on both morphological and physiological adaptations to cope with Mediterranean environmental constraints. In such ecosystems, vegetation is composed by perennial, summer deciduous, or seasonally dimorphic species. Plants of Cistus spp. adopt seasonal dimorphic habitus with mesic winter and xeric summer leaves and represent an effective model to study temperature acclimation. This work aimed to evaluate the eco-physiological response of Cistus salvifolius L. winter leaves (WL) to high temperatures since in a climate change scenario, winter temperature is expected to increase of 5°C in the Mediterranean Basin. Plants grown outdoor at winter temperature (hardened) were transferred at +10 °C in a greenhouse to induce the de-hardening. Photosynthetic fast-response curves to light, CO2 and temperature as well as fast light fluorescence curves were performed on: WL grown outdoor (WLO); WL grown outdoor and moved indoor for 15 days (WLI_15); WL developed indoor (WLI). SLA and LDMC were also determined. WLO showed lower photosynthetic rate, apparent carboxylation efficiency and mesophyll conductance than WLI. In these leaves an higher partitioning of absorbed light in photochemistry than in thermal dissipation was also measured together with lower SLA and higher LDMC values. The growth of WL at higher temperatures determines a rise of photosynthesis and an increase of light utilization in dissipative processes together with SLA reduction.