Physiological and biochemical responses of Quercus brantii seedlings to water deficit stress

Water shortage is one of the most important environmental stresses in Mediterranean regions. Poor seedling quality may account for the failure of oak regeneration. To determine the best seed origin of Quercus brantii, we investigated on seedlings collected from 20 mother trees in the Zagros Mountain forests 700 to 2200 m altitudes above sea level. Seedlings from different altitudes were irrigated at 25%, 50%, 75% and 100% of field capacity (FC), from June through the end of August 2005, and then their growth, physiological and biochemical parameters were examined. The results showed that the activity of peroxidase (PO), superoxide dismutase (SOD), and amylase, as well as the rate of membrane lipid peroxidation and the content of lignin were not affected by water deficit stress. However, the survival and growth rates were reduced below 50% FC. Seedlings originated from lower altitudes had higher growth and survival rate than those from higher altitudes below 50% of FC. The seedlings grown under 50% FC had also high phosphorus and water soluble carbohydrate contents. In conclusion, the present study showed that the seedlings from lower altitudes, which their mother trees grown under warmer climate condition in growth season, were more resistant to water deficit due to higher root to shoot ratio, phosphorus and water soluble carbohydrate contents under water deficits.