Objective To understand the response to salt stress on rice varieties cultured at different nitrogen levels.

Method Two north japonica rice varieties were cultured at five nitrogen levels of nutrient solution until booting stage, the changes of biomass, photosynthetic characteristics and some physiological characteristics of two rice varieties were measured in three salt concentrations.

Result and conclusion The biomass of rice varieties which were cultured at different nitrogen levels of nutrient solution decreased under salt stress; there were significant decrease in net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and apparent mesophyll conductance (AMC) of rice leaves under salt stress. The Pn reduction was due to non-stomatal restriction factors in low-nitrogen-level nutrient solution, however, the stomatal and non-stomatal limitation factors resulted in the Pn reduction in high-nitrogen-level nutrient solution. Under salt stress, the activity of antioxidant enzymes such as SOD, POD and CAT, the contents of proline and soluble sugar of leaves in 1/2N-level nutrient solution were significantly higher than those at other nitrogen-levels, the membrane permeability and the content of MDA in 1/2N-level were lower than those at other nitrogen-levels. The results show that rice varieties cultured in 1/2N-level nutrient solution can improve the capacity of osmotic regulation, enhancing the salt-tolerance ability of rice varieties at booting stage. The capacity of salt-tolerance of Jiudao13 is higher than that of Jijing88.