| Cd(Cadmium)is one of the most widely polluted heavy metals with the strongest biological toxicity;Zn(Zinc)is not only an essential trace element in plants,but also an important element in heavy metal pollution.The single and compound pollution of Cd and Zn is becoming more and more serious,which has a great threat to the ecological environment and human health.So it's urgent to restore and manage the polluted soil.Ryegrass(Lolium perenne)and tall fescue(Festuca arundinacea)are two kinds of perennial cold season turfgrass widely planted in urban greening.They both have good trampling resistance,strong regeneration and adaptability.There have been some researches on their ability to repair the soil polluted by Cd and Zn,but researches on their compound stress are still few.Therefore,in this experiment,the growth and enrichment characteristics of ryegrass and tall fescue under Cd,Zn stress were studied by setting different concentration gradients of Cd,Zn single and compound pollution treatment in pot experiments,and the improvement effect of combined strengthening measures on the enrichment of two plants was also explored.Cd concentration of single pollution A1-A5: 5,10,50,100,150 mg / kg;Zn concentration of single pollution B1-B5: 50,100,400,600,800 mg / kg.Cd concentration of compound pollution A1-A3: 10,50,100 mg / kg;Zn concentration of compound pollution B1-B3: 100,400,800 mg / kg.The results are as follows:(1)Under the single stress of Cd and Zn,the germination and growth indexes of ryegrass were inhibited,negatively correlated with the metal concentration,andshowed strong differences in the medium and high concentrations of Cd in A3-A5 and Zn in B3-B5 mg / kg.The germination and growth indexes of tall fescue were also inhibited,but the germination rate and biomass were not significantly affected.Besides that,other indexes all showed significant differences in high concentration of A5 Cd and B5 Zn.In general,ryegrass and tall fescue have some tolerance to Cd and Zn.(2)Under different concentrations of Cd-Zn compound stress,the germination potential and germination rate of ryegrass and tall fescue were inhibited,and the germination rate obtained the minimum value at A2B3,which was significantly different from the control.The growth of shoot and root of the two plants were also inhibited in different degrees,among which the shoot growth of ryegrass was inhibited more than tall fescue,and the growth of root of two plants were both significantly inhibited.The biomass of ryegrass and tall fescue obtained the minimum values at A3B3 and A2B3 respectively.The cell membrane permeability and proline content of ryegrass were increased compared to the control.The chlorophyll content and photochemical efficiency of ryegrass,and the chlorophyll content of tall fescue basically decreased compared with the control.The optimal values of each physiological index were all obtained under A3 Cd or B3 Zn,indicating that the two plants were under strong stress at high concentration of Cd and Zn.(3)In the compound pollution of Cd and Zn,the accumulation of Cd in ryegrass and tall fescue were positively correlated with Zn concentration in A3 Cd,and the maximum value was obtained in A3B3.The bioconcentration factor(BCF)of Cd of ryegrass had the maximum value at A2B1.At the same Cd concentration,BCF(Cd)of tall fescue was positively correlated with Zn concentration,and the maximum value was obtained at A3B3.The BCF(Cd)of ryegrass was higher than that of tall fescue,and the BCF(Cd)of the root was higher than that of the shoot.The translocation factor(TF)of Cd of ryegrass and tall fescue reached the maximum at A1B2 and A2B2 respectively.The Zn accumulation and BCF(Zn)of the two plants were positively correlated with Cd concentration at B2 and B3,and the maximum value was obtained at A3B3.The TF(Zn)of ryegrass were significantly higher inA1B1 and A3B3 than in the control,and had the maximum value in A1B1.In B1-B3 treatment,the TF(Zn)of tall fescue reached the maximum in group under the high Cd concentration of A3,and sorted as: A3B1 > A3B3 > A3B2.(4)Under the combined pollution of Cd and Zn,lime significantly promoted the growth of ryegrass and tall fescue,while continuous cutting and citric acid had different effects on the growth of seedlings among the three strengthening measures.Lime significantly promoted the biomass accumulation of ryegrass and the root of tall fescue,but significantly inhibited the biomass accumulation of the shoot of tall fescue in A1B3 and A3B1,while continuous cutting and citric acid basically inhibited the biomass accumulation of the two plants.(5)Under the effect of the three strengthening measures,the Cd accumulation in the shoot and root of ryegrass showed a decreasing trend.The BCF(Cd)of ryegrass was significantly promoted in A1B3 and inhibited in A3B1.The BCF(Cd)of the shoot of tall fescue was significantly promoted at A1B3 and inhibited at A3B3,and the BCF(Cd)of the root was just inhibited by continuous cutting and citric acid.In general,the significant effects of the three strengthening measures on the TF(Cd)of ryegrass and tall fescue were all promoting.Lime inhibited the Zn accumulation of ryegrass most significantly,while citric acid promoted that significantly in A3B3.The accumulation of Zn in tall fescue was promoted by the strengthening measures in B1 Zn but inhibited in B3 Zn.The BCF(Zn)of ryegrass was significantly inhibited by continuous cutting and lime.The BCF(Zn)of tall fescue was significantly influenced by citric acid,increasing in A3B1 but reducing in A3B3.The TF(Zn)of ryegrass was significantly inhibited by citric acid in A1B3,and significantly promoted by three measures in A3B1 while citric acid has the strongest influence,and significantly inhibited by cutting and lime in A3B3.The TF(Zn)of tall fescue increased significantly in A1B3 under the influence of lime and reduced significantly in A3B1 and A3B3 by the three strengthening measures. |
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