Climate change poses a major threat to Mediterranean forests by increasing temperature and radiation stress. To support adaptive afforestation strategies, we investigated the physiological performance of key native and introduced tree species commonly planted in Israel. Our goal was to define the thermal optima for carbon assimilation (Topt), assess sensitivity to high light, and quantify carbon sequestration potential under variable temperature regimes. Ten species were grown in controlled-environment chambers under four day/night temperature regimes (34/28°C, 28/22°C, 22/16°C, 22/10°C). We used gas exchange measurements to capture the core processes of the plant carbon cycle— photosynthesis and respiration—and evaluated leaf-level carbon dynamics. These were combined with chlorophyll fluorescence and growth measurements to assess stress responses. Additionally, stable carbon (δ13C) and oxygen (δ18O) isotope analyses were used to estimate intrinsic water-use efficiency and long-term carbon assimilation across temperatures.
Ziziphus spina-christi showed the highest photosynthetic capacity and performed best above 30°C, with stable isotope data supporting its high carbon gain and water-use efficiency. In contrast, species such as Pinus halepensis and Ceratonia siliqua showed reduced photosynthesis and growth above 28°C, indicating vulnerability to warming. Among Acacia species, A. elatior demonstrated exceptional biomass accumulation (30–60% higher than others), broad thermal tolerance, and strong carbon uptake under both low and moderate temperatures. However, it was highly sensitive to photoinhibition at high irradiance (>1500 μmol photons m−2 s−1). A. raddiana thrived under the hottest conditions, while A. tortilis was optimal at intermediate temperatures. Surprisingly, all species showed substantial radiation sensitivity, even those from arid environments. Our results define species-specific Topt and reveal important trade-offs between heat tolerance, light stress, and carbon assimilation, offering a physiological framework for selecting climate-resilient trees that support long-term carbon sequestration in future Mediterranean forests.
