Abstract:

【Objective】Salt content is usually unevenly distributed in saline-alkali lands. Studies on growth and development, and the changes of physiological and biochemical indexes of sorghum seedlings under non-uniform salt stress could provide a theoretical basis for the cultivation of sorghum in saline-alkali land and the efficient exploitation and utilization of saline-alkali lands.【Method】Roots of sorghum were divided into two equal portions by a root-split method and put in uniform and non-uniform NaCl concentration solution, respectively. There were four treatments. No sodium chloride (denoted as 0/0) was the control, 0 and 200 mmol·L ^-1(denoted as 0/200), 50 mmol·L ^-1 and 150 mmol·L ^-1(denoted as 50/150) were non-uniform salinity treatments, and 100 mmol·L ^-1/100 mmol·L ^-1 (denoted as 100/100) were uniform salinity treatment. Healthy sorghum seedlings after growing for 14 days in a growth chamber were sampled for the determination of biomass, leaf area, SPAD, root morphology, osmotic regulators content, anti-oxidative enzyme activity, and photosynthetic parameters. 【Result】 Growth of sorghum both in uniform and non-uniform salt stress conditions was severely inhibited, and significant decrease of fresh weight, biomass, leaf area, root morphology, photosynthetic capacity, anti-oxidative enzyme activity and osmotic substance content accumulation was found. Dry weight per plant was increased by 21.19% and 62.71%, fresh weights of seedlings was increased by 35.39% and 86.44%, and leaf area was increased by 13.22% and 88.66%, respectively under 50/150 and 0/200 compared with those under 100/100. Under 50/150 treatment, fresh and dry weights of roots in the 50 mmol·L ^-1 side were 1.90 and 2.10 times of the 150 mmol·L ^-1 side. Under 0/200 treatment, fresh and dry weights of roots in 0 mmol·L ^-1 side were increased by 3.02 and 3.75 times compared with the 200 mmol·L ^-1 side. Likewise, local root morphology was affected significantly in non-uniform salt treatment. Root length, root volume, root tip number, and root branch number of sorghum seedlings in 50 mmol·L ^-1 side or 0 mmol·L ^-1 were significantly increased compared with 150 mmol·L ^-1 (50/150) or 200 mmol·L ^-1 (0/200) salt stress side, respectively. Root length, root volume, root tip number, and root branch number of the whole root were significantly increased under 0/200 (P<0.05) compared with the 100/100 treatment. Activities of SOD, CAT, and POD in leaves were significantly higher under non-uniform salt stress (P<0.05). Contents of proline and soluble sugars were significantly increased in leaves with a dramatic reduce in MDA content (P<0.05) under the non-uniform salinity treatments. Compared with seedlings under the 100/100 condition. Photosynthesis of sorghum was significantly enhanced under 0/200 and 50/150 salt stresses, which chiefly was reflected by notably increased photosynthetic rate, stomatal conductance, transpiration rate, and decreased intercellular CO₂ concentration (P<0.05). With respect to indexes of fluorescence of photosynthesis, such as ΦPSⅡ, Fv/Fm, and ETR, their values under 50/150 and 0/200 were increased by 5.64% and 19.00%, 9.25% and 18.89%, and 1.93% and 6.89%, respectively. ΦPSⅡ and Fv/Fm under 0/200 were significantly different from those under 100/100 (P<0.05).【Conclusion】Both non-uniform and uniform salt stress treatments caused growth inhibition to sorghum seedlings. However, due to the root compensatory growth of low salt or salt-free side under the non-uniform salt stress condition, whole root morphology, leaf antioxidant enzymes activity, osmotic regulation ability, and photosynthetic capacity were improved in a certain degree. Thus, non-uniform salinity could relieve damages to sorghum seedling initiated by salt stress.

Key words: sorghum bicolor, split root, non-uniform salinity, photosynthesis, fluorescence