Effects Of Exogenous Hydrogen Sulfide On Seed Germination And Seedling Physiology Of Sweet Clover Under Salt Stress

In order to study the ability and dose effect of hydrogen sulphide?H₂S?to enhance the resistance of forage underNaCl stress,the appropriate spraying concentration and spraying times were selected.The sweet clover?Melilotus suaveolens?was used as material.The seeds and seedlings of sweet clover under NaCl stress were treated with H₂S donor sodium sulphide?NaHS?by hydroponic method to study the effect of H₂S treatment on the seed germination and seedling physiology of sweet clover under NaCl stress,and investigate the relief mechanism of growth and development of sweet clover seedlings with H₂S treatment under NaCl stress.The results are as follows:?1?The relative germination rate,relative germinating potential,seedling growth potential and salt tolerance index of sweet clover seeds under NaCl stress were increased by soaking seeds with certain concentration of NaHS for 12 h,and the effect of NaHS seed soaking at different concentrations was significant.The comprehensive evaluation of membership function method showed that 0.2 mmol·L^-1 had the best effect,and the 0.8mmol·L^-1 was the worstamong the 6 kinds of NaHS concentration soaking treatments of sweet clover seeds under NaCl stress(150 mmol·L^-1).?2?NaHS treatment could increase the relative water content and decrease the relative electrical conductivity of the leaves of sweet clover seedlings under NaCl stress,so as to alleviate the damage to the cell membrane of sweet clover;and NaHS treatment could reduce the accumulation of free proline caused by salt stress,increase the content of soluble sugar and soluble protein,and enhance the activity of antioxidant enzyme,and,decrease the content of malondialdehyde.?3?The effects of different concentrations of NaHS treatment on alleviating NaCl salt stress of sweet clover were significantly different.With the increase of concentration,the changes of each index were different,but each index showed a certain dose effect.The comprehensive effect of different treatments was evaluated by using membership function method.The results showed that 0.1 mmol·L^-1 had the best mitigation effect,followed by 0.2mmol·L^-1 among the 6 kinds of NaHS concentration treatment of sweet clover seedlings treated with NaCl salt stress(150 mmol·L^-1).?4?NaHS treatment could increase the content of chlorophyll a,chlorophyll b and the total chlorophyll content under NaCl stress,reduce chlorophyll fluorescence parameters Fo,NPQ,increase Fv/Fm,Fv/Fo,qP and?PSII,and also reduce the stomatal and non stomatal limitations under salt stress,increase the rate of transpiration and water use efficiency,and increase the use efficiency of water.And the net photosynthetic rate of sweet clover seedlings was increased.NaHS treatment also increased the fresh weight,plant height and root length of sweet clover seedlings.?5?The effect of different NaHS spraying times on on alleviating NaCl stress of sweet clover were significantly different,and the changes of chlorophyll,chlorophyll fluorescence,photosynthetic parameters and growth index were different under different spraying times.For the sweet clover seedling under 150 mmol·L^-1NaCl stress,spraying with 0.1 mmol·L^-1concentration NaHS,on the first day,the 7th day,the 14th day?T3 treatment?is the most reasonable treatment.