Evaluation of radiation use efficiency of superior clones of Salix based on photosynthetic light-response characteristics.

We determined the photosynthetic light-response curves of 51 clones of Salix using modified rectangular hyperbola model in order to analyze their characteristic parameters of photosynthetic light-response. The results showed that at the beginning of light increase, there were no distinct differences in the photosynthetic rate among the clones; as the light intensity continued to increase, the net photosynthetic rate (Pn) of each clone peaked and then declined nonlinearly, of which, net photosynthetic rates of clones Q43, Q31and SH48 were apparently higher than those of other clones or species. The maximum net photosynthetic rate (Pnmax) of Q43 was the highest (32.50 μmol/(m2·s)) among 51 superior clones, and that of S. erioclada the lowest, 11.74 μmol/(m2·s). The dark respiration rate (Rd) of the clone 2462 was the lowest (0.43 μmol/(m2·s)), while that of S. babylonica was 9 times higher. Light compensation points (LCP) of clones 84 and 2462 were low, which were 7.47 and 8.70 μmol/(m2·s), and light saturation point (LSP) of Salix sp. was the highest (1 996.48 μmol/(m2·s)). The principle component analysis suggests that the four indexes could be summarized as two principle components, contributing 81.494%. The 51 clones were divided into four types according to the principle component analysis, and the result was verified by measuring annual growth of height and branch diameter of the four types of Salix. It is suggested that the superior clones in type Ⅰ, with a wide range of use of light, have the strongest adaptation ability to environment, higher radiation use efficiency and the biggest annual growth, and thus were elite high light-efficiency ones.