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Effects of NaCl stress on substances linked to osmotic adjustment and on photosynthetic physiology of Melilotoides ruthenica in the seedling stage
- YAO Jia, LIU Xin-Bao, CUI Xin, LI Zhi-Hua
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2015, 24(5):
91-99.
DOI: 10.11686/cyxb20150511
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The effects of various levels of NaCl stress [0 (control), 50, 100, 150, 200, 250, 300 mmol/L] on the osmotic adjustment matters and photosynthetic physiology of Melilotoides ruthenica seedlings were investigated in pot experiments. Soluble protein and sugar contents of seedlings decreased with increasing NaCl concentration. However, proline content increased with increased NaCl concentration. The contents of soluble protein, sugars, and proline differed under different salt concentrations and stress exposure times. On the 7th day and 14th day after imposing stress, soluble protein contents of seedlings exposed to 300 mmol/L NaCl concentrations were significantly lower than those of controls (P<0.05). On the 7th, 14th and 21st day after imposing stress, soluble sugar contents of seedlings exposed to 50 or 100 mmol/L NaCl concentration were higher than those of the controls, while on 28th day after stress, soluble sugar contents of seedlings exposed to 250 or 300 mmol/L NaCl concentrations were significantly lower than those of the controls (P<0.05). On the 7th day after imposing stress (150-300 mmol/L NaCl), the 14th day after imposing stress (200-300 mmol/L NaCl) and on the 28th day after imposing stress (250 or 300 mmol/L NaCl), the proline content was significantly higher than that of the control and other treatments (P<0.05). Hence under salt stress, three indicators of osmotic adjustment had different time signatures. With increases in both NaCl concentration and stress exposure time, the physical damage to M. ruthenica seedlings became more serious, while photosynthetic parameters varied with NaCl concentration and stress exposure time. On the 14th day after imposing stress, photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs) and intercellular CO2 concentration (Ci) increased at low, and decreased at high salt concentration. Pn, Tr, and Gs of seedlings under 50-100 mmol/L concentrations were significantly higher than those of control plants, while Pn and Tr of seedlings under 300 mmol/L were significantly lower than those of control plants and of other treatments (P<0.05). On 28th day after imposing stress, Pn, Tr, Gs and Ci were decreased with increasing of salt concentrations. On the 14th and 28th days after imposing stress, stomatal limitation (Ls) and water use efficiency (WUE) increased with increasing NaCl concentration.
