Effects Of Exogenous Melatonin On Growth And Physiological Characters Of Alfalfa Under Drought Stress

In abiotic stress,drought is a very important factor limiting the growth of alfalfa.Potting method was used to study the different concentrations of melatonin(0,0.05,0.10,0.15,0.20 mmol/L)for different water conditions(normal water supply-80%field water holding capacity,mild stress-60%field water holding capacity,Moderate stress-40%field water holding capacity,severe stress-20%field water holding capacity).Growth,antioxidant enzyme activity,photo synthetic characteristics,cell membrane stability and osmotic substances of alfalfa(Medicago sativa)in the branching and bud stage And the effects of alfalfa yield and quality during the bud stage.The research results are as follows:Exogenous melatonin treatment had an effect on the plant height,stem diameter and number of branches of alfalfa in the branching and bud stage.With the deepening of drought stress,the plant height,stem diameter and branch number of alfalfa showed a downward trend.At the branching stage,melatonin at 0.05,0.10,and 0.15 mmol/L significantly increased stem diameter and number of branches under mild,moderate,and severe drought.In the bud stage,0.10 mmol/L melatonin can significantly increase plant height and stem diameter under mild and moderate drought;0.15 mmol/L significantly increase plant height,stem diameter and number of branches under severe drought.Exogenous melatonin treatment had an effect on the antioxidant enzyme activity and malondialdehyde(MDA)content of alfalfa in the branching and bud stage.With the deepening of drought stress,the activities of superoxide dismutase(SOD),catalase(CAT),peroxidase(POD)in leaves increased first and then decreased,while MDA The content is on the rise.At the branching and bud stage,0.10 mmol/L of melatonin can significantly increase the activity of SOD and CAT,and significantly reduce the level of MDA under mild and moderate drought stress.Under severe drought stress,0.15 mmol/L fades.Melanin significantly increased SOD and CAT activities under severe stress and significantly decreased MDA content.Exogenous melatonin treatment had an effect on the photosynthetic characteristics and chlorophyll content of alfalfa in the branching and bud stage.During mild and moderate drought stress,net photosynthetic rate(Pn),transpiration rate(Tr),intercellular CO2 concentration(Ci),stomatal conductance(Gs)and chlorophyll content decreased with increasing drought stress.The stomatal limit value(Ls)increased continuously;in severe stress,Pn,Tr,Gs,and chlorophyll content decreased,while Ci and Ls increased.Under the mild and moderate stress,0.10 mmol/L melatonin had the best effect on increasing Pn,Ci,Gs and Tr and significantly increased chlorophyll content in the branching and bud stage.Under severe stress,0.15 mmol/L melatonin has the best effect on increasing Pn and chlorophyll content of alfalfa.Exogenous melatonin treatment has an effect on the permeability and electrolyte permeability of alfalfa in the branching and bud stage.In the mild and moderate drought stress,with the deepening of drought stress,free proline,soluble protein,soluble sugar content and electrolyte permeability increased continuously;in severe stress,free proline,soluble protein and The electrolyte permeability increases while the soluble sugar decreases In the branching and bud stage,under mild and moderate drought,0.10 mmol/L melatonin can significantly increase the content of soluble sugar,soluble protein and free proline in alfalfa,and reduce the electrolyte permeability;Under severe stress,0.15 mmol/L melatonin significantly increased the content of these permeates and significantly reduced the electrolyte permeability.Exogenous melatonin treatment has an effect on the yield and quality of alfalfa in the bud stage.With the deepening of drought stress,fresh grass yield,hay yield,crude protein,crude fat and crude ash of alfalfa showed a decreasing trend,and acidic detergent fiber and neutral detergent fiber showed an increasing trend.Under mild and moderate drought,0.10 mmol/L melatonin significantly increased the yield of fresh grass and dry matter,crude protein,crude fat and crude ash,and reduced the content of acid detergent fiber;under heavy stress,0.15 mmol/L faded Melanin works better for these indicators.