Physiological Response And Rhizosphere Characteristics Of Malva Pusilla To Cadmium Stress

Phytoremediation is a kind of soil remediation technology with ecological environment protection and broad application prospect,which application is based on the tolerance of heavy metals.The hyperaccumulator is few,and most of which have small biomass,slow growth and low ornamental value.Compared with hyperaccumulator,Malva pusilla SM have relatively large biomass,high ornamental value,good ecological adaptability and wide garden application basis,which are a good material for plant restoration practice.The aim of this research is to explore the physiological response and cadmium accumulation characteristics of Malva pusilla to cadmium stress.A controlled pot-experiment was arranged with different treatments of different cadium concentrations[0(CK),5,15,30,60,100 mg/kg] to investigate the effect of different level of cadmium treatment,and the absorption of mineral elements,growth physiology and the changes of main rhizosphere characteristics of Malva pusilla.this study used pot experiments to study the absorption of mineral elements,growth physiology and the changes of main rhizosphere characteristics of Malva pusilla under different concentrations of cadmium[0(CK),5,15,30,60,100 mg/kg].Providing a theoretical basis for its application in urban cadmium contaminated soil treatment.The main results are as follows:(1)Comparing with control,the biomass of Malva pusilla increased significantly(P<0.05).The absorption of mineral elements changed with Cd concentration increasing.The increasement of biomass was as follows: leaf>stem>root.The total accumulation of cadmium was as follows: above ground>below ground.Cadmium treatment promoted the absorption and accumulation of Ca,Fe,Mn and Cu in the roots and stems of Malva pusilla,and the differences were significant(P<0.05);however,the absorption of Ca,Fe,Mg and Mn in the leaves was inhibited under high cadmium concentration(≥60 mg / kg),and the content of Cu in the leaves had no significant effect.(2)Under cadmium treatment,the protective enzyme system of Malva pusilla was activated,and the content of antioxidants increased.The activities of antioxidant enzymes(SOD,POD,CAT)increased with the increasement of Cd concentration,and the differences between the treatments were significant(P<0.05).The contents of GSH and ASA in roots increased significantly(P<0.05)with the increasement of Cd concentration,while the contents of GSH and ASA in leaves increased first and then decreased,but both of them were higher than the control.The content of soluble sugar in roots increased significantly(P<0.05),while the content of soluble sugar in leaves was lower than that in the control with the high concentration of cadmium(≥60 mg/kg);the content of soluble protein in roots and leaves increased first and then decreased,and the differences between treatments were significant,and reached the peak at the concentration of 30mg/kg cadmium.(3)The activities of catalase and sucrase in the rhizosphere soil of Malva pusilla were significantly higher than those of the control(P<0.05)under different concentrations of cadmium,and their activities increased with the increasement of cadmium concentration.The differences between the treatments were significant.The p H of rhizosphere soil was significantly lower than that of the control under cadmium stress(P<0.05),but the p H of non rhizosphere soil had no significant change.(4)Under cadmium treatment,the order of organic acid secretion content was citric acid,oxalic acid,fumaric acid,malic acid,succinic acid,tartaric acid,malonic acid,pyruvic acid,lactate and acetic acid.Cadmium treatment significantly increased the contents of oxalic acid and citric acid in plant roots(P<0.05).The correlation analysis showed that the contents of organic acids,citric acid and oxalic acid in roots were positively correlated with the cadmium accumulation ability of Malva pusilla(P<0.001).The contents of malic acid,fumaric acid and tartaric acid increased first and then decreased with the increase of cadmium concentration.In conclusion,different concentrations of cadmium promoted the growth of Malva pusilla.In addition,the increasement of organic acid secretion in the roots of Malva pusilla may be one of the reasons for its high tolerance to cadmium.The higher the concentration of cadmium,the more organic acid secretion,the lower the p H value of rhizosphere soil,the higher the solubility of mineral elements in the soil,and promote the absorption of mineral elements in the roots of Malva pusilla.