| In this research,a Petri dish experiment and pot test were conducted to determine the effect of salicylic acid(SA)pretreatment on the seed germination,seedling growth conditions,physiological characteristics,photosynthesis,cationic distribution in different organs and forage quality of alfalfa(Medicago sativa)under different NaCl concentrations(0%,0.3%,0.6%,0.9%,and 1.2%).Seeds and seedlings were preprocessed by immersing and spraying with solutions of 0,0.5,1.5,and 2.5 mM SA for 24 h and 3 days,respectively.These samples were then cultured in a growth chamber and outdoors.We usedMedicagoLinn ’Weston’ which treated with NaCl to studythe effect of SA on plant’s germination,growthand saline tolerent physiology.The research contents and results were listed as follows:1.The germination of alfalfa was significantly affected by different concentration of SA under NaCl stress.Under the fixed SA concentration,analysis results of the different NaCl levels effect on the germination parameters showed that the seed germination rate at SO and S0.5 levels and vigor index at S1.5 and S2.5 levels as well as seedling and root length at S0.5 level at first increased,then decreased as the increase of NaCl concentrations.Under the fixed level of NaCl stress,the analysis results of the different SA treatments effect on the germination was as follows:Treated with 0.5mmo1·L-1SA significantly increased seed germination rate,germination potentials and index at 0.9%and 1.2%levels of NaCl,root length and vigor index at 0.6%and 1.2%levels of NaCl,and seedling length at 0.6%levels of NaCl comparison with the control(P<0.05).Application of 1.5 mmol·L-1SA significantly increased vigor index and seedling length at 0.6%levels of NaCl,germination rate and seedling length at 0.9%levels of NaCl,and seed germination rate,germination potentials and index at 1.2%levels of NaCl compared with the control(P<0.05).However,2.5mmol·L-1 SA did not obviously improved seed germination,and inhibited the germination by exacerbation of some inhibitory effects.These results indicated that the treatments of 0.5～1.5mmol·L-1 SA improved the alfalfa seed germinationin varying degrees and relieved the NaCl stress on alfalfa seed germination.2.The effects of different concentration of SA on plant height,stem diameter,branch number,root dry weight per plant,dry weight per plant and leaf dry weight per plant of alfalfa were dependent on the levels of SA and NaCl as well as exposure time.The analysis results of different SA concentration on plant growth at fixed NaCl concentration was as follows:the treatment of 0.5mmol·L-1 SA significantly enhanced plant heights in 7d-28d of 0.6%NaCl stress,branch numbers on the 21st day of 0.3%NaCl stress,stem and leaf dry weight per plant on the 28th day at NaCl levels within the range of 0.3%～0.9%,root dry weight per plant at 0.3%and 0.9%levels of NaCl compared with the control(P<0.05).The treatment of 1.5 mmol·L-1 SA significantly increased root dry weight per on the 28th day of 0.9%NaCl stress,stem dry weight per plant on the 28th day at 0.3%NaCl stress,andleaf dry weight per plant on the 28th day at 0.6%and 1.2%levels of NaCl compared with the control(P<0.05).The above results indicated that appropriate SA concentration can relieve various NaCl stress on alfalfa growth.3.The physiological characteristics of alfalfa was significantly affected by different concentration of SA under NaCl stress.Under fixed level of SA,the changes of various physiological characteristics of alfalfa were investigated at different NaCl levels,results of which was as follow:in the 4 periods of NaCl stress,relative water content(RWC)of alfalfa leaf decreased with the increasing of NaCl concentrations;The relative electroconductibility(EL),malondialdehyde(MDA)and proline(Pro)contents increased with the increasing of NaCl concentrations.During the whole period of NaCl stress,the activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)at first increased,and then decreased.The effects of different SA concentrations on various parameters under the fixed concentration of NaCl were explored.The results was as follows:The treatment of 0.5 mmol·L-1 SA significantly increased the RWC on 7th and 14th days of 0.3%NaCl stress comparison with the control(P<0.05).The treatment of 1.5 mmol·L-1 SA significantly decreased EL on 7th,14th,and 21st days of 0.9%NaCl stress compared with the control(P<0.05).Application of 0.5 and 1.5 mmol·L-1 SA significantly decreased the MDA from 14th to 28th days under 0.6%NaCl stress,and MDA on 28th day of 1.2%NaCl stress compared with the control(P<0.05).What’s more,presence of 0.5 and 1.5 mmol·L-1 SA significantly enhanced SOD and POD activities on 28th day of 0.3%NaCl stress,POD activities,soluble sugar content,and Pro content on 14th day under 0.6%NaCl stress,CAT activities and Pro content on 14th day of 1.2%NaCl stress,and soluble protein content on 7th day of 1.2%NaCl stresscompared with the control(P<0.05).4.In different periods,the photosynthetic parameters of alfalfa was significantly affected by different concentration of SA under NaCl stress.Under the fixed level of SA,the changes of various photosynthetic parameters of alfalfa were investigated at different NaCl levels,results of which was as follow:with the increase of NaCl concentration,the chlorophyll content on the 14th day of stress at different SA levels,the photosynthetic rate(Pn)in 14～28 days at various SA levels,the stomatal conductance(Gs)in 21～28 days at various SA levels,the water use efficiency(WUE)on 7th day of treatment S0,and the transpiration rate(Tr)and intercellular CO2 concentrations(Ci)in all periods of stress were decreased,however,the stomatal limitation(Ls)decreased during the whole periods.Under fixed level of NaCl,the effects of different SA levels on photosynthetic parameters were investigated,results of which was as follow:The treatment of 0.5 mmol·L-1 SA significantly increased chlorophyll content on 7th day of 0.6%NaCl stress,and chlorophyll content on 14th day of 0.3%NaCl stress compared with the control(P<0.05).Both treatments of 1.5 and 2.5 mmol·L-1 SA significantly increased chlorophyll content on 7th and 14th days of 0.9%NaCl stress(P<0.05).The treatment of 0.5 mmol·L-1 SA significantly increased Pn and Tr on 21st day of 0.9%NaCl stress,Ci on 14th and 21st days of 0.6%NaCl stress,and WUE on 28th day of 0.3%NaCl stress compared with the control(P<0.05),and significantly decreased Ls on 14th and 21st days of 0.6%NaCl stress.The treatment of 1.5 mmol·L-1 SA significantly increased Pn on 7th day of 0.6%and 1.2%NaCl stress,Gs and Ci on 21st day of 0.9%NaCl stress(P<0.05),and significantly decreased Ls on 14th and 21st days of 0.6%and 0.9%NaCl stress compared with the control(P<0.05).5.On the 28th day of stress,Na+content in root,stem,and leaf of alfalfa increased with the increase of NaCl concentration,and reached maximum value at 0.9%and 1.2%levels of NaCl.Under fixed level of SA,K+content in leaf at all levels of SA and in stem at level of S0.5 at first increased,and then decreased,and K+content in leaf at NaCl levels of 0.3%-0.9%significantly increased(P<0.05).K+contents in stem at levels of S0,S1.5,and S2.5,and in root at all levels of SA presented downtrend.Under the fixed level of NaCl,the plants were treated with different concentrations of SA.On the 28th day of treatment,0.5 and 1.5 mmol·L-1 SA significantly decreased Na+ contents in leaf and stem of alfalfa under 0.6%level of NaCl stress,and Na+ contents in root and stem under 0.9%level of NaCl stress,compared with the control(P<0.05).Meanwhile,Na+contents in root,stem,and leaf under 0.3%levels of NaCl stress were also significantly decreased by 0.5 mmol·L-1 SA in comparison with the control(P<0.05).Compared with the control,K+content in root under 0.3%level of NaCl stress,and in stem and leaf under 0.6%and 0.9%levels of NaCl stress were significantly enhanced by 1.5 mmol·L-1 SA(P<0.05).6.Yield and quality of forage were investigated under fixed concentration of SA and different levels of NaCl stress.The results were as follow:at all of SA levels,crude protein(CP),ether extract(EE),crude ash(CA)content,hay yield and quantity of crude protein were all decreased with the increase of NaCl level,and were significant lower than those of NO under NaCl levels of 0.6%～1.2%(P<0.05);Neutral detergent fiber(NDF)and acidic detergent fiber(ADF)presented downtrend with the increasing of NaCl levels,and reached maximum value at NaCl levels of 0.9%and 1.2%(P<0.05).Application of 0.5 mmol·L-1 SA significantly enhanced CP content,EE content,as well as hay yield and quantity of crude protein of alfalfa under 0.3%NaCl stress compared with the control(P<0.05),furthermore,NDF and ADF were significantly reduced by 0.5 mmol·L-1 SA under 0.3%level of NaCl stress(P<0.05).Compared with the control,presence of 1.5 mmol·L-1 SA significantly enhanced the CP content,CA and EE contents(dry matter based)under 0.9%levels of NaCl stress,hay yield under 0.6%and 1.2%levels of NaCl stress,as well as the quantity of crude protein under 0.6%and 1.2%levels of NaCl stress(P<0.05).In addition,NDF under 0.9%and 1.2%levels of NaCl stress and ADF under 0.6%level of NaCl stress were significantly decreased by 1.5 mmol·L-1 SA(P<0.05). |
PDF Full Text Request