Effects Of Lead And Cadmium Single And Compound Stresses On The Physiological And Enrichment Characteristics Of Viola Prionantha

The perennial herb Viola prionantha is a ground cover plant with certain ornamental value,strong adaptability and resistance in Northeast China.With the development of heavy industry,the pollution of heavy metals lead(Pb²⁺)and cadmium(Cd²⁺)has become more and more serious in recent years.Plants have been exposed to heavy metal pollution for a long time,and their growth and physiology are affected,which in turn leads to the reduction of landscape benefits.The important herbaceous cover plants in landscaping have high application value,but there are few related studies on anti-heavy metal pollution,and the mechanism of heavy metal resistance is still unclear.Cd²⁺single and its compound stress hydroponic experiment（hydroponic experiment has stronger controllability of solution concentration and easier recovery of heavy metals than soil culture experiment）to study the growth physiological indexes and the absorption and transfer of heavy metal elements of Viola prionantha under heavy metal stress Changes in properties and other aspects,the concentrations are 5,10,15,30,50 mg·L^-1(Cd²⁺),10,25,50,100,200 mg·L^-1(Pb²⁺),and the results are as follows:1.The change trend of leaf length,leaf width and other growth indicators of Viola prionantha under different concentrations of Cd²⁺stress showed that the low concentration had little effect,and the high concentration showed a gradually increasing inhibitory effect.At the end of the treatment,the leaf length,leaf width and leaf area of Viola prionantha were 18.98%,19.50%and 31.06%lower than Ck.The antioxidant enzymes SOD,POD and CAT of Viola prionantha under Cd²⁺stress were similar in changes.The activities of SOD,POD and CAT showed a trend of first increase,then slowing down and then decreasing with the increase of Cd²⁺stress concentration.The content of Pro,MDA,soluble sugar and soluble protein increased continuously with the increase of Cd²⁺treatment concentration.2.The leaf length,leaf width and leaf area of Viola prionantha under different concentrations of Pb²⁺were affected in different degrees.Compared with Ck at the end of the treatment,the highest reduction was 18.18%,15.84%and 30.03%.Pb²⁺stress had a small promotion at low concentration and inhibition effect at high concentration on leaf length,leaf width and leaf area of Viola prionantha.Under the low concentration of Pb²⁺stress,the changes of growth indexes were not obvious,but the higher the concentration of Pb²⁺,the more obvious the inhibited degree of growth indexes.The activities of antioxidant enzymes SOD,POD and CAT in Viola prionantha under low concentration Pb²⁺stress increased with the increase of Pb²⁺stress concentration,and then the rate of increase slowed down or even started to decrease.The activities of SOD,CAT and POD started to decrease in high concentration Pb²⁺treatment from the 15th day of treatment.The content of Pro,soluble sugar and MDA increased gradually with the increase of Pb²⁺stress concentration,while the content of soluble protein showed a gradual decrease,and the change trend was similar to the Cd²⁺treatment group.3.The growth indexes of Viola prionantha under the compound stress of different concentrations of Pb²⁺and Cd²⁺showed a stronger inhibitory effect than the single stress of Pb²⁺and Cd²⁺.It showed a high degree of reduction,with the highest reductions of 19.71%,19.28%,and 34.52%compared with Ck.The induction and promotion effect of Pb²⁺and Cd²⁺compound stress on the antioxidant enzymes CAT and POD of Viola prionantha was higher than that of Cd²⁺and Pb²⁺group,and the induction effect of SOD was lower than that of Pb²⁺group but higher than that of Cd²⁺.The promoting effect on Pro and soluble sugar content was higher than that in Pb²⁺,Cd²⁺single stress group,the inhibitory effect on soluble protein was higher than that in Pb²⁺,Cd²⁺single stress group,and the promoting effect on MDA content was lower than that in Pb²⁺,Cd²⁺single stress group.4.The results of photosynthesis test showed that the changes of each photosynthetic index and light response parameters were basically the same under the single and compound stress treatments of Pb²⁺and Cd²⁺.On the whole,with the increase of heavy metal concentration,the contents of P_n,G_s,T_rand chlorophyll gradually decreased,and the contents of Pb²⁺and Cd²⁺The lowest contents of P_n,G_s,T_rand chlorophyll in the compound treatment group were29.87%,49.91%and 49.91%of Ck,respectively.45.26%,35.36%.C_igradually increased with the increase of the treatment concentration.The highest is 1.55 times of Ck.The light response parameters P_nmax,LSP,R_dand AQE gradually decreased with the increase of the treatment concentration,while LCP increased gradually.5.The results of absorption and enrichment experiments showed that the absorption and enrichment laws of Viola prionantha under single and compound stress of Cd²⁺and Pb²⁺were similar.Generally,the content of heavy metals in the roots of the underground was higher than that in the stems and leaves of the shoots.At the same time,with the increase of the concentration of heavy metals,its transport coefficient gradually decreased,and the absorption and enrichment efficiency of heavy metals also gradually decreased.The content of Pb²⁺and Pb²⁺were lower than the amount absorbed under single stress.It can be seen that Cd²⁺and Pb²⁺have a certain degree of antagonism in the absorption and enrichment of heavy metals in Viola prionantha.According to the test results,Viola prionantha has certain resistance to Cd²⁺and Pb²⁺,and its resistance mechanism is similar,so Viola prionantha can be applied to low concentrations of Cd(0-10mg·kg^-1),Pb(0-50mg·kg^-1)in slightly Cd²⁺,Pb²⁺polluted areas.