Abstract: 【Objective】Soil salinity is spatially heterogeneous. The effects of heterogeneous salinity on the growth, water uptake, photosynthetic parameter, K⁺ and Na⁺ concentration in leaf and root of alfalfa plants were determined to improve understanding of non-uniform salt stress tolerance mechanisms of alfalfa, so as to provide theoretical evidence for breeding the new alfalfa varieties tolerant to salt, and to improve alfalfa plant in salinity areas. 【Method】 Plant growth, water uptake, tissue ionic concentrations were studied in alfalfa plants grown hydroponically for 7 days using a split-root system, with uniform 0 and 200 mmol·L^-1 NaCl or heterogeneous 0/400 and 100/300 mmol·L^-1 NaCl. 【Result】 Neither uniform salinity or heterogeneous salinity inhibited alfalfa growth, decreased water uptake, increased leaf Na⁺ concentration and decreased leaf K⁺ concentration. Compared with uniform 200 mmol·L^-1 NaCl, 0/400 treatment significantly increased the alfalfa shoot fresh weight and whole plant water uptake. Shoot fresh weight and whole plant water uptake under 0/400 treatment were 24.3% and 44.2%, respectively, higher than 200/200 treatment. The leaf Na⁺ concentration in 0/400 treatment was 53.6% lower than in 200/200 treatment, and the leaf K⁺ concentration was similar with 200/200 treatment . But water uptake in non-salinity root was 12.3% higher and Na⁺ concentration in non-salinity root of 0/400 treatment was 10.5-fold higher than control, whereas K⁺ concentration in non-salinity root of 0/400 treatment was similar with control. There were no significantly differences of shoot fresh, water uptake and leaf K⁺ concentration between 100/300 and 200/200 treatment, but leaf Na⁺ concentration in 100/300 treatment were 31.0% higher than in 200/200 treatment. Water uptake were 33.9% lower, K⁺ concentration was 31.3% lower, and Na⁺ concentration were 39.5-fold in low-salinity root of 100/300 treatment, compared with control. Transpiration rate, stomatal conductance and intercellular CO₂ concentration of 0/400, 100/300 and 200/200 treatment were similar with each other and significantly lower than control, however, net photosynthetic of 0/400 and 200/200 were significantly higher than control, and net photosynthetic of 100/300 were similar with control.【Conclusion】When root average salinity was 200 mmol·L^-1 NaCl, the NaCl concentration of high salinity root were equal or greater than half lethal concentration, heterogeneous salinity can improve alfalfa plant growth when low salinity root under 0 mmol·L^-1 NaCl, but heterogeneous salinity can not improve alfalfa plant growth when low salinity root under 100 mmol·L^-1 NaCl.

Key words: alfalfa, heterogeneous salinity, water uptake, Na⁺ regulation, photosynthetic parameter