| In order to explore the effects of salicylic acid on alfalfa of different growth periods under dif-ferent drought stresses.The pot experiment was conducted to determine the effects of the different concentrations[0(The control),0.02,0.10,0.50,2.50 mmol/L]of salicylic acid on the growth,the physiology characteristics and photosynthetic characteristics of Medicago sativa in the branching,bud and early flowering stage under different water stresses[normal water supply(80%of field capacity),mild drought stress(60%of field capacity),moderate drought stress(40%of field capacity),heavy drought stress(20%of field capacity)].The main results are as following:In the branching stage,with the increasing intensity of-drought stress,plant height,stem diameter,branch number,leaf relative water content were reduced gradually.Photosynthetic rate(Pn),transpiration rate(Tr)and stomatal conductance(Gs),interecellular CO2 concentration(Ci)also showed a trend of reduced gradually.Chlorophyll content,superoxide dismutase(SOD)activity increased firstly and decreased in severe water stress.Soluble sugar content was reduced firstly and increased in severe water stress.Malondialdehyde(MDA)content,relative electric conductivity,peroxidase(POD)activity,catalase(CAT)activity,soluble protein content,proline content,water use efficiency(WUE),stomatal limitation value(LS)were increased gradually.The effect of salicylic acid on alfalfa was different under different drought stress.Under mild drought stress condition,CAT activity and Gs were significantly increased in the treatment with 0.10 mmol/L salicylic acid;CAT activity was significantly increased in the treatment with 0.50 mmol/L salicylic acid.Under moderate drought stress,soluble protein content,POD and CAT activity were significantly increased in the treatment with 0.10 mmol/L salicylic acid,but Ls was decreased;plant height,CAT activity,proline and soluble protein content of alfalfa were significantly increased in the treatment with 0.50 mmol/L salicylic acid,Ls was decreased.Under severe drought stress,plant height,stem diameter,leaf relative water content,CAT activity,Pn,Tr,Ci and Gs were significantly increased in the treatment with 0.10 mmol/L salicylic acid,but Ls was decreased.;plant height,stem diameter,leaf relative water content,SOD activity POD activity,soluble protein,soluble sugar content and Gs were significantly increased in the treatment with 0.50 mmol/L salicylic acid,but Ls was significantly decreased.In the bud stage,with the increasing intensity of drought stress,only the soluble sugar content was reduced gradually,and other indicatiors were similar with branching stage.Under the condition of normal water supply,salicylic acid had no significant effect on alfalfa.Under mild drought stress condition,chlorophyll content,SOD and POD activity were significantly increased in the treatment with 0.50 mmol/L salicylic acid.Under moderate drought stress,branch number,POD activity,CAT activity,soluble protein content,Pn and Gs significantly increased in the treatment with 0.10 mmol/L salicylic acid,but leaf relative electrical conductivity and Ls were decreased;plant height,stem diameter,branch number,leaf relative water content,POD activity,CAT activity,Gs,proline and soluble protein content of alfalfa were significantly increased in the treatment with 0.50 mmol/L salicylic acid,but leaf MDA content and Ls were significantly reduced.Under severe drought stress,plant height,leaf relative water content,SOD,POD and CAT activity,soluble protein,soluble sugar content,Tr and Ci were significantly increased in the treatment with 0.10 mmol/L salicylic acid,but leaf MDA content and leaf relative conductivity and Ls were significantly reduced.;plant height,stem diameter,leaf CAT activity,soluble protein content,soluble sugar content and Pn were significantly increased in the treatment with 0.50 mmol/L salicylic acid,Ls was decreased;acidleaf proline content of alfalfa was significantly increased in the treatment with 2.50 mmol/L salicylic.In the early flowering stage,with the increasing intensity of drought stress,the fresh grass yield,dry matter yield,the content of crude protein(CP),ethanol extract(EE),crude ash(CA)content and in vitro dry matter digestibility(IVDMD)of alfalfa were reduced gradually,but chlorophyll,neutal detergent fiber(NDF)and acid detergent fiber(ADF)content were increased gradually,other indicatiors were similar with branching stage.The effect of different salicylic acid treatments on alfalfa under different drought stresses in early flowering stage as following.Under the condition of normal water supply,salicylic acid had no significant effect on alfalfa.Under mild drought stress condition,IVDMD was significantly increased in the treatment with 0.10 mmol/L salicylic acid,NDF content was decreased;CAT activity and CA content were significantly increased in the treatment with 0.50 mmol/L salicylic acid.Under moderate drought stress,branch Number,fresh grass yield,soluble protein content,dry matter,Ci and IVDMD were significantly increased in the treatment with 0.10 mmol/L salicylic acid,but Ls was significantly reduced;stem diameter,chlorophyll content,proline content,EE,CA content,SOD,POD,CAT activity,fresh grass yield,dry matter yield soluble protein content,IVDMD and Ci were significantly increased in the treatment with 0.10 mmol/L salicylic acid,but relative conductivity,MDA content and Ls were significantly reduced.Under severe drought stress,soluble protein content,proline content,fresh grass yield,dry matter yield,IVDMD,Pn,Tr and POD,CAT activity were significantly increased in the treatment with 0.10 mmol/L salicylic acid;plant height,chlorophyll content,fresh grass yield and dry matter yield,CAT and SOD activity,soluble protein content,proline content and IVDMD were significantly increased in the treatment with 0.50 mmol/L salicylic acid,but leaf relative conductivity,Ls,NDF and ADF content were decreased significantly.In conclusion,the suitable concentrations of salicylic acid can improve the drought resistance ability of alfalfa. |
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