A Study of Photosynthetic Characteristics and Leaf Traits of Salix cupularis with Different Ages in Alpine Sandy Land

Salix cupularis is the main plant for windbreak and sand fixation in northwest Sichuan. In this study, investigations were made on the differences of photosynthetic capacity and leaf traits among four age-class seedlings (1-, 2-, 8- and 11-year-old) of S. cupularis. The photosynthesis parameters and light response curves were measured using portable Li-6400 photosynthetic system (Licor, USA). The results showed that the diurnal variation of net photosynthetic rate (P_n) of S. cupularis showed an unimodal curve without midday depression. The P_n of 2-year-old S. cupularis was significantly higher than that of others, and the order was nursery 2-year-old > wild 11-year-old > nursery 1-year-old > nursery 8-year-old. The daily variation trend of G_s and T_r were the same, and the daily mean value of 2-year-old S. cupularis in nursery were higher than the other three age classes. The diurnal variation value of L_s showed the lowest in the morning, the L_s daily mean value of 2-year-old S. cupularis was lower than that of 1-year-old S. cupularis in nursery and 11-year-old S. cupularis in wild, and there was no significant difference compared with 8-year-old S. cupularis in nursery. WUE daily mean value of 11-year-old S. cupularis in wild was significantly higher than that of the other three age-class S. cupularis. P_{n max} of 2-year-old S. cupularis was significantly higher than that of others. LCP and R_d of 1-year-old S. cupularis were lower than that of the other three age-class S. cupularis. LCP and LSP of 11-year-old S. cupularis in wild were significantly higher than others in nursery. Leaf dry matter content of 11-year-old S. cupularis in wild was significantly higher than others in nursery. Leaf area, leaf dry weight, specific leaf area of 1-year-old S. cupularis in nursery and 11-year-old S. cupularis in wild were significantly lower than those of 2-year-old and 8-year-old S. cupularis in nursery.