The Tolerance Thresholds And Accumulation Ability To Soil Cadmium Contamination In Warm Season Turfgrasses

Cadmium soil pollution causes not only toxic effects to plants but also serious harm to animal and human health through the food chain. In recent years, the emergence and development of phytoremediation technology has provided a new approach for the treatement of cadmium soil pollution. In this study, Zoysiagrass(Zoysia japanica) and Hybrid bermudagrass(Cynodon dactylon×Cynodon transvadlensis) were used to evaluate the growth and physiological responses under series of concentrations of Cb stresses in the pot experiments. The tolerance thresholds of Cd in Zoysiagrass and Hybrid bermudagrass were also discussed. Meanwhile, centipedegrass (Eremochloa ophiuroides) and seashore paspalum (Paspalum vaginatum) were used to study the influence of absorption and transfer efficiency of cadmium after applying chelating agents into the soil .The main results were indicated as follows:(1) The physiological responses and tolerance threshold of Zoysiagrass and Hybrid bermudagrass were investigated under eight different Cd concentration(0, 60, 120, 180, 240, 300, 360,and 420mg/ kg)in a sand culture system.The results showed that biomass in Zoysiagrass did not show significant changes under 60mg/kg compared with the control, relative growth rate(RGR),turf quality,photochemical efficiency(Fm/Fv)and leaf chlorophyll content in Zoysiagrass did not show significant changes under 120mg/kg compared with the control,and leaf electrolyte leakage(EL)in Zoysiagrass did not show significant changes under 180mg/kg compared with the control;Biomass,relative growth rate(RGR),turf quality,photochemical efficiency(Fm/Fv)and leaf chlorophyll content in Hybrid bermudagrass did not show significant changes under 60mg/kg compared with the control ,and leaf electrolyte leakage(EL) in Hybrid bermudagrass did not show significant changes under 120mg/kg compared with the control.Regression analysis was used to determine the threshold Cd concentration for each physiological parameter and the most sensitive parameter occurred by biomass of 98mgCd/kg in Zoysiagrass and 81mgCd/kg in Hybrid bermudagrass ,and the two values were chosen as the Cd tolerance threshold in Zoysiagrass and Hybrid bermudagrass,respectively,because under this concentration the plant did not show any significant difference with the control in all growth and physiological parameters measured in this experiment.(2) The absorption and distribution characteristics to soil cadmium contamination were studied in a sand culture experiment in Zoysiagrass and Hybrid bermudagrass. The results showed that the Cd concentrations in leaf,stem and root increased along with the increase of Cd concentration, the Cd accumulation of stem which was the highest reached 12249 mg/kg DW and 8622 mg/kg DW respectively, and,followed by the roots which was 5583 mg/kg DW and 4227mg/kg DW respectively, and the lowest of Cd accumulation in leaf which was 3751 mg/kg DW and 1961 mg/kg DW respectively. Different soil cadmium concentration treatment also affect the transport of Cd from root to leaf in Zoysiagrass and Hybrid bermudagrass, the transport coefficient of Zoysiagrass reached the maximum 0.855 at Cd concentration 180mg/kg, and the transport coefficient of Hybrid bermudagrass reached the maximum 0.756 at Cd concentration 120mg/kg.(3) Centipedegrass and seashore paspalum were used to study the influence of absorption and transfer efficiency of cadmium after applying chelating agents EGTA,NTA,EDTA and citric acid into the soils. The results showed that chelating agents had a negative effect on the biomass of the both turfgrass species. EGTA had a minor effects on the biomass with no significant affect in seashore paspalum and a significant affect on root biomass of centipedegrass. NTA,EDTA and citric acid affected the biomass of root, stem and leaf in both turfgrasses significantly. EGTA increased the Cd concentration in the leaf but decreased in the stem and root in both turfgrasses, which resulted a slight increase of transport coefficient. NTA significantly increased the Cd concentration of root in seashore paspalum but the increase was not reach the significant level in centipedegrass. Citric acid increased the Cd concentration of root but decreased the Cd concentration of stem and leaf in both turfgrasses. The results indicated that EGTA could promote the transportation of Cd from stem and root to leaf, and citric acid could promote the Cd accumulation in the root.