Effects of Enhanced UV-B Radiation on Photosynthetic Parameters and Dark Respiration of Populus yunnanensis and P.szechuanica

We compared the leaf photosynthetic parameters, dark respiration rate and leaf thickness of Populus yunnanensis and P. szechuanica originating from altitudes of 2 430 m and 3 300 m,respectively,when exposed to enhanced ultraviolet-B (UV-B) radiation: 2.5 and 5 kJ/(m2d). These enhanced UV-B intensity were provided by ultraviolet lamp based on simulation of 10% and 20% ozone depletion in Kunming area. Results showed that enhanced UV-B radiation significantly reduced Net photosynthetic rate (Pn) by 32% and 51% in P. yunnanensis, by 16% and 39% in P. szechuanica, respectively. In contrast, dark respiration rate (Rd) and leaf thickness of both species were significantly increased. Correlating analysis indicated that there were significantly positive correlation between Pn and WUE, and negative correlation between Pn and Rd (P0.01).On the other hand, 2.5 kJ/(m2d) UV-B treatments had different influences on stomatal conductance, Rd and Rd/Pn of both study species.Moreover, Pn,Rd and leaf thickness were significantly larger in P.szechuanica than in P.yunnanensis. Therefore,it could conclude that P.szechuanica from high altitude had a greater tolerance to enhanced UV-B environment than P.yunnanensis from low altitude.