Effects Of Heavy Metal Cd And Zn On Seed Germination And Seedling Growth In Alfalfa

Heavy metal pollution repair has become one of the difficult problems in environmental management.Based on the perennial growth characteristics with high biomass and strong regenereation,alfalfa has great potential to be used in phytoremediation of heavy metal polluted environment,and it is important for alfalfa seeds to establish under heavy metal polluted conditons.In this paper,alfalfa cultivar Algonquin was selected to test the effects of heavy metal cadmium and zinc on seed germination and seedling growth using the petri dish germination methods.Different concentrations of CdCl2(0,5,10,20,40,80 and 160 mg/L),ZnSO4(0,30,60,120,240 and 480 mg/L)and Cd/Zn combined treatments have been studied.The results were as below:1.Under the treatment of low concentration of CdCl2(5 mg/L),alfalfa germination potential and seed germination rate were 94.40�0.98%and 96.00� 1.26%,respectively,and no significant difference was found compared to the control group.The germination potential and germination rate were greatly decreased 13.82%and 8.94%as the concertration of CdCl2 was 40 mg/L(p<0.05).It was found significantly difference of germination potential and germination rate compared to the control group when treated with concentration of CdCl2 between 10 mg/L and 40 mg/L.As the concertration of CdCl2was 160 mg/L,the germination potential and germination rate were 64.80�3.44%and 64.80�3.44%,respectively.Under the treatment of low concentration of CdCl2(5 mg/L),alfalfa vigor index and germination index were 650,33�25.10 and 20.05 � 0.30,respectively,and no significant difference was found compared to the control group.On the contrary,the seed vigor index and germination index significantly decreased when treated with CdCl2 between 10 mg/L and 40 mg/L.As the concertration of CdCl2 was 40 mg/L,the seed vigor index and germination index were 186.48 �11.04 and 17.30�0.56,respectively.As the concertration of CdCl2 was 160 mg/L,the vigor index was 54.41 �2.94.and the germination index was greatly decreased 45.02%(p<0.05).Treated with different concentrations of CdCl2 under time to seeds germination significantly effected seedling root length,shoot length,root fresh and shoot fresh weight,and which is the same to the seedling root length,bud length and root fresh mass(p<0.001).It is seedling root growth inhibition degree was greater than the growth of seedling bud when treated the concentrations of CdCl2.2.Under the treatment of low concentration of ZnSO4(30 mg/L),alfalfa germin-ation potential and seed germination rate were 93.60�0.98%and 95.20� 1.50%,respectively,and no significant difference was found compared to the control group.The germination potential and germination rate were greatly decreased 32.23%and 29.51%as the concertration of ZnSO4 was 240 mg/L(P<0.05).It was found significantly difference of germination potential and gerrmination rate compared to the control group when treated with concentration of ZnSO4 between 60 mg/L and 240 mg/L.As the concentration of ZnSO4 was 480 mg/L,the germination potential and germination rate were 52.00� 1.26%,52.80�0.80%,respectively.Under the treatment of low concentration of ZnSO4(30 mg/L),alfalfa vigor index and germination index were 697.55�71.44 and 17.71 �0.54,respectively,and no significant difference was found compared to the control group.On the contrary,the seed vigor index and germination index significantly decreased when treated with ZnSO4 between 60 mg/L and 240 mg/L.As the concertration of ZnSO4 was 240 mg/L,the seed vigor index and germination index were decreased 72.23%and 33.88%,respectively(P<0.05).The vigor index and germination index were 102.77�4.06 and 9.77�0.21,respectively,as the concertration of ZnSO4 was 480 mg/L.Treated with different concentrations of ZnSO4 under time to seeds germination significantly effected seedling root length,shoot length,root fresh and shoot fresh weight,and which is the same to the seedling root length,bud length,root fresh mass and bud fresh mass(P<0.001).3.As the concertration of CdCl2 was 40 mg/L,the germination potential,germination rate,vigor index and germination index were no significant difference was found compared to the control group when treated with concentration of ZnSO4 between 60 mg/L and 240 mg/L.The results indicated that it was reduced the toxicity of Cd with the increased of concentration of ZnSO4.As the concertration of CdCl2 was 80 mg/L and ZnSO4 was 480 mg/L,the germin-ation potential and germination rate were decreased 57.72%and 57.61%,respectively(p<0.05).And the seed vigor index and germination index were 24.54�1.23 and 6.25�0.16,respectively.When treated with different complexes concentrations of Cd/Zn under time to seeds germination significantly effected seedling root length,shoot length,root fresh and shoot fresh weight,and which is the same to the seedling root length,bud length,root fresh mass and bud fresh mass(p<0.001).In a word,on one hand heavy metal Cd,Zn,Cd/Zn pollution caused seeds germination and growth of seeding with low concentrations and stimulating effect on inhibition effect of high concentrations,and inhibition of seedling root growth to a greater extent than the growth of seedling bud.As the concertration of CdCl2 was 40 mg/L,it could effectively reduced Cd on the toxicity of alfalfa when treated with concentration of ZnSO4 between 60 mg/L and 240 mg/L;on the other hand the results of above all would provide useful reference for soil test in future,and it also opens a new perspective for the study of phytoremediation species selection.