The compensation growth and salt ion distribution in sweet sorghum (Sorghum bicolor L. Moench) after salt stress reduction

Adversity compensation effect is ubiquity in crops, which impacts on crop growth, development and yield. To elucidate the compensation growth of sweet sorghum following soil salt stress reduction, a pot experiment was conducted, in which 5 gkg^-1 (high salt), 2 gkg^-1 down from 5 gkg^-1 (salt stress reduction) and 2 gkg^-1 (low-salt control) of soil salt treatments were applied at the elongation stage of sweet sorghum. Then growth rate of dry matter on aboveground parts (leaf, leaf sheath and stem) and aboveground dry matter at maturity of two cultivated sweet sorghum varieties were determined. The experiment also measured salt ions (K⁺, Na⁺ and Cl^-) distribution in aboveground organs of sweet sorghum. The results showed that the growth rate of aboveground dry matter in high salt treatment was always significantly lower than that of control. There was clear acceleration of growth after soil salt reduction, and gradually exceeded the growth of control due to overcompensation effect. At maturity stage, both plant height and aboveground dry matter of two sorghum varieties decreased sharply in high salt treatment. They decreased by 7.69% and 33.21%, respectively, in ‘Liaotian 1’ in salt stress reduction treatment compared with the low-salt control, moreover, no obviously difference was found in both plant height and aboveground dry matter of ‘Zhongketian 3’ between salt stress reduction treatment and low-salt control. The contents of Na⁺ and Cl^- in aboveground organs significantly increased, and K⁺ content slightly increased under high salt stressed condition. At 35 days after soil salt reduction, the contents of Na+ and Cl^- still higher than that of low-salt control, but decreased significantly compared to that of high salt treatment. Although K⁺ content in both leaf sheath and stem in soil salt reduction treatment were higher than that of low-salt control, no difference was observed in leaf. The results suggested that ion toxicity in salt-stressed sweet sorghum alleviated after soil salt reduction, and the growth rate eventually exceed that of low-salt control due to overcompensation effect, especially, for salt-tolerance cultivar ‘Zhongketian 3’. This provided the theoretical basis for sweet sorghum cultivation in saline-alkali soils.