Effect of altitude on photosynthesis rate and some physiological indices from three species of Quercuis brantii, Pistacia atlantica, Crataegus pontica in Ilam province forests

Increasing the altitude causes extensive changes in the environmental conditions. Three species of Quercus brantii Lindl., Pistacia atlantica Desf. and Crataegus pontica C. Koch. are the dominant species in the forests of Ilam province. The sampling was done from Qalajeh Mountain at the altitude from 1300-2000 m a.s.l. The effect of altitude on photosynthesis, photosynthetic pigments and some biochemical parameters (proline, soluble sugars, proteins, antioxidant enzymes) of these plant species were investigated. The results indicated that with increasing the altitude, the photosynthetic parameters (net photosynthesis and transpiration) and photosynthetic pigments decreased in the three species. A significant positive correlation was observed between photosynthetic parameters and photosynthetic pigments. The results showed that with increasing altitude, the total soluble sugar and proline content significantly increased, that this value was higher in Q. brantii and P. atlantica than the C. pontica. Furthermore, a significant negative correlation was observed between photosynthetic parameters and the total soluble sugar and proline in P. atlantica and Q. brantii species. Regarding to the antioxidative enzymes, a significant difference was determined only in P. atlantica and the activity of antioxidant enzymes in P. atlantica was more regular than others. Overall, it could be concluded that with increasing altitude and decreasing photosynthesis and photosynthetic pigments, the amount of compatible soluble compounds (total soluble sugar and proline) and antioxidant enzymes increased as a mechanism for plants adaptation against stress conditions.