Effects of soda salinealkaline stress on photosynthesis and growth of Nitraria sibirica

The growth, gas exchange parameters and chlorophyll fluorescence parameters were investigated in Nitraria sibirica under the soda salinealkaline stress in pots. The results showed that moderate soda salinealkaline contents in soil could stimulate biomass and growth of N. sibirica. At a level of 0.2% soda salinealkaline content in soil, the biomass peaked, 27.3%higher than that of the control. Under high levels of soda salinealkaline stress, the net photosynthetic rate declined, mainly due to nonstomatal limitation factors and partially due to the decrease in leaf water content and chlorophyll content. The increase of intercellular CO2 concentration under high levels of soda salinealkaline stress might result partially from the nonuniform stomatal closure. The content of carotenoid dropped at a low level of soda salinealkaline content in soil but lifted at higher levels, while NPQ showed no significant differences under various levels of soda salinealkaline stress. It is suggested that a high level of NPQ in N. sibirica could be kept by increasing the content of carotenoid. There were significantly positive correlations between biomass and Pn, LUE, CUE, stomatal limitation value (Ls), Fv/F0, Fv/Fm (P0.01). The primary indices that could be used to evaluate the tolerance of N. sibirica to soda salinealkaline stress are biomass, Pn, LUE, CUE, Fv/F0 and Fv/Fm, while the secondary ones include Ls and Fm. The effectiveness of the indices depends on the type of salts in soil.