Abstract: Effects of different concentrations of La(NO₃)₃ on growth of ryegrass seedlings and regulatory effect on photosynthetic physiological response in ryegrass leaves under 150 mmol·L^-1 NaHCO₃ stress were investigated. The ryegrass leaves were sprayed by low concentration(0.05 mmol·L^-1) of La(NO₃)₃ solution for 3 days before NaHCO₃ stress. The results showed that La(NO₃)₃ pretreatment significantly alleviated the decreases of the fresh and dry weights of ryegrass seedlings, the leaf chlorophyll and carotene contents, the activities of Hill reaction, electron transport, photophosphorylation, Mg²⁺ATPase and RuBPCase in chloroplast, and photosynthetic rate by alkaline stress, but no effect on glycolic acid oxidase activity was observed. However, pretreatment of La(NO₃)₃ with high concentration(0.5 mmol·L^-1) had no alleviation effect on alkaline stress, instead, aggravated the injury by alkaline stress on ryegrass seedlings. These results suggested that the pretreatment of feasible concentration of La(NO₃)₃ could alleviate the inhibitory effect on the growth of ryegrass seedlings by alkaline stress via improving leaf photosynthetic function.

Key words: La(NO₃)₃, alkaline stress, ryegrass, seedling growth, photosynthetic physiology