The Effect of Water Stress on Gas Exchange in Two Iranian Oak Species (Quercus brantii) and V yvl (Quercus libani)

Drought is the major environmental stresses that it can have a negative impact on plant growth. The study of gas exchange under drought stress can help to identify factors affecting stress resistant. Due to this fact that Zagros forests has Mediterranean and dry climate, with the aim of this study was to assess the impact of drought on leaf gas exchange in two oak species (Quercus brantii and Quercus libani). Water stress consisted of four levels of water stress (100%, 70%, 50% and 30% FC) in the greenhouse situations. Those seedlings were intended for water stress weren’t irrigated to reach to the desired field capacity (70%, 50% and 30% of field capacity), but control seedlings were irrigated every day in order to soil water content at field capacity shall be kept 100%. Results showed that water stress treatment has a significant reduction of stomatal conductance, photosynthesis, conduct mesophilic, carbon dioxide emission, and transpiration. Also Quercus libani showed higher level of photosynthesis, water use efficiency and transpiration than Quercus branti. Overall, results in both species, showed stomatal and non-stomatal limitation would cause of photosynthesis reduction. Also, due to higher water efficiency and lower gas parameter variations, Quercus libani would gain better mechanism of waster stress and Quercus brantii would gain the use drought avoidance mechanism.