| In this study,a petri dish method and a pot method were conducted to study the effects of different NaCl concentrations(0%,0.3%,0.6%,0.9%,1.2%)on seed germination,growth characteristics of alfalfa including Coated Magna 995,Weston,Blue moon and Ghillie,and to explore the change regulation of antioxidant enzyme system,osmotic adjustment substances and photosynthesis in alfalfa under NaCl stress condition.The main results are as follows:1.The relative germination rate,relative germination potential,seedling growth potential and salt tolerance index of 4 alfalfa varieties were significantly negatively correlated with the increase of the salt concentration(P<0.01).Meanwhile,with the increase of salt concentration,the decline of both relative germination potential and relative germination rate were the smallest in Coated Magna 995,and were the largest in Weston.0.3%of NaCl improved the seedling growth of the 4 varieties,and the seedling growth was inhibited when the NaCl concentration exceeded 0.3%.The seedling growth potential of Weston was higher than that of other 3 varieties when the the NaCl concentration was less than 1.2%.The results of salt tolerance evaluation of 4 varieties showed that the order of salt tolerance was 4 Coated Magna 995'>'Weston'>'Ghillie'>'Blue moon' during the germination period.2.The salt stress inhibited the growth of 4 alfalfa varieties.Furthermore,the different concentrations of NaCl promoted the the biomass of underground,but significantly inhibited the biomass of aboveground.With the increase of NaCl concentration,the plant height were decreased,while the stem diameter were first increased and then decreased.When the concentration of NaCl was 0.3%,the stem diameter was significantly higher than that of control(0%)(P<0.05);However,when the NaCl concentration was higher than 0.3%,both of the plant height and stem diameter of the 4 varieties were significantly lower than that of the control(P<0.05).Therefore,when the NaCl concentration exceeded 0.3%,the growth of alfalfa was inhibited.3.The relative water content of leaves were decreased with the extension of stress time,while the relative conductivity of leaves were increased.The relative conductivity of Coated Magna 995 and Ghillie became significantly higher than that of control(P<0.05)on the 7th days of trteatment,and the relative water content of leaves became significantly lower than that of the control(P<0.05)on the 14th days of trteatment;However,the relative conductivity of Weston and Blue moon was started to be significantly higher than that of control(P<0.05)on the 14th days of trteatment;In addition,there was no significantly difference between the relative water content of leaves in treatment groups and in control from the beginning to end(P>0.05).4.With the extension of stress time,all of SOD,POD,CAT activity and MDA content showed an increasing trend.Compared with the control,the activities of SOD and POD became higher on the 7th days of trteatment(P<0.05).With the different trends of CAT activity in different varieties,the CAT activity of Coated Magna 995 was significantly higher than that of control on the 7th to 21th days(P<0.05).While the CAT activity of Weston was significantly higher than that of control(P<0.05)on the 14th day of treatment.Furthermore,there was no significantly difference between the CAT activity in treatment groups and in control on the 7th to 21th days(P>0.05).5.NaCl stress inhibited the photosynthesis of alfalfa.With the extension of stress time,the chlorophyll content showed an increasing trend.The chlorophyll content of the 4 varieties were significantly lower than that of the control on the 14th days of trteatment(P<0.05).In addition,the photosynthetic rate,all of transpiration rate,stomatal conductance,intercellular CO2 concentration and water utilising efficiency were significantly lower than that of the control on the 28th days of trteatment(P<0.05),while the stomatal limitation were significantly higher than that of the control(P<0.05).6.With the extension of stress time,all of soluble sugar,soluble protein and free proline content showed an increasing trend.The changes of soluble sugar content in Coated Magna 995,Blue moon and Ghillie were consistent,which became higher than that of the control on the 14th day of treatment(P<0.05);While the soluble sugar content of Blue moon was significantly higher than that of the control in all observation periods(P<0.05).Moreover,the free proline content of Coated Magna 995 and Weston were significantly higher than that of the control in all observation periods(P<0.05). |
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