Abstract:

Effects of salt stress on photosynthetic characteristics of 1-year-old potted mulberry (Morus alba) seedlings, a common stock of mulberry, were investigated. The seedlings were treated with NaCl concentrations at 0.1%,0.3%,0.5% and 0.7%, fresh water as the control. Using LI-COR 6400 portable photosynthesis system, the net photosynthetic rate (P_n）, stomatal conductance（G_s）, intercellular CO₂ concentrations（C_I） and transpiration rate（T_r） were measured on 1^st,2^nd,3^rd and 7^th day after treatments, and the light response curves and the CO₂ response curves of the net photosynthetic rate were measured on 3^rd day after treatments. The results showed that 0.1% NaCl did not affects the photosynthetic characteristics of the seedlings, however, while salt concentration≥0.3%, the salinity significantly reduced P_n, G_s, T_r, WUE,SUE and CUE, but enhanced C_I. P_n under 0.1% NaCl treatments was a little bigger than that of the control. Under lower salt concentration treatments, P_n decrease was mainly controlled by the stomatal limits, whereas under higher salt concentration treatments, P_n decrease was mainly due to the non-stomatal limits. The net photosynthetic rate under various treatments all gradually increased with PAR or CO₂ concentration increasing, however, effects of PAR or CO₂ concentration on P_n significantly varied among different NaCl concentration treatments. It was showed that effects of them on P_n decreased with NaCl concentration increasing. In addition, salinity also had an obvious impact on the light compensationpoint（LCP）, light saturation point（LSP）, apparent quantum yield（AQY）, apparent maximum photosynthetic rate（P_max）, the CO₂ compensation point（LCP）and apparent carboxyl efficiency (ACE). In general, P_max, AQY,LSP, CCP and ACE decreased, but LCP increased with NaCl concentration increasing.

Key words: mulberry stock, salt stress, photosynthetic characteristics, light response, CO₂ response