Effects of partial root salt stress on seedling growth and photosynthetic characteristics of winter wheat

Most studies on plant salt stress have generally been conducted under uniform salinity in the root zone. However, the distribution of salinity in the soil is not always uniform under natural settings. Winter wheat is one of the main crops grown in salt-affected soils in China, with seedlings sensitive to salt stress. The effects of partial root salt stress on the growth and photosynthetic characteristics of winter wheat seedlings were investigated in this study using a split-root system in hydroponic culture. Each half root of the wheat seedlings was treated with either uniform (0|0 mmol L^-1, 75|75 mmol L^-1 and 150|150 mmol L^-1) or non-uniform (0|150 mmol L^-1) concentrations of NaCl, resulting in total or partial root salt stress. The results showed that salt stress significantly inhibited the growth of winter wheat seedlings, which inhibition increased with increasing NaCl concentration. Compared with total root salt stress treatments 150|150 mmol L^-1 and 75|75 mmol L^-1, partial root salt stress (0|150 mmol L^-1) increased shoot dry weight by 23.5% and 17.2%, respectively. Partial root salt stress compensated for root growth in none salt-stress conditions by increasing root length, lateral root number and lateral root length respectively by 195.2%, 206.2% and 237.8% over that in 150 mmol L ^-1 NaCl condition. In the 0|150 mmol L^-1 treatment, root Na⁺ content in 150 mmol L^-1 NaCl side of the treatment dropped significantly by 12.1% than that in either sides of 150|150 mmol L^-1 treatment. Also root Na⁺ content in salt-free side of 0|150 mmol L^-1 increased significantly over that in either sides of the 0|0 treatment. These results indicated that increased Na⁺ in roots in the salt-free side was possibly transported from the 150 mmol L^-1 NaCl side of the treatment. Partial root salt stress treatment also decreased Na⁺ concentration in roots and leaf Na⁺/K⁺ content. Also P_n, G_s, C_i, T_r and chlorophyll fluorescence parameters (F_v/F_m) were higher in 0|150 mmol L^-1 treatment than in total root salt stress. The improvement in plant growth under partial root salt stress was attributed to the reduction in leaf Na⁺ concentration and Na⁺/K⁺ ratio and the related increase in photosynthesis.