Lead Tolerance And Accumulation In Turfgrass

Lead is one of the chief heavy metals in contaminated soils. Soils contaminated with lead have significant impact on human health, especially for children. Physical and chemical techniques for repairing of contamined soils are costs and not environment-friendly, and may cause second pollution and can't remove heavy metals completely sometimes. The phytoremediation is a cost-effective"green"technology based on the use of hyperaccumulating plants to remove heavy metals from the soil. The main lead contaminated soils are located in the city and industrialized zones. Turfgrasses are main plant species used in urban landscape, thus, using turfgrasses in phytoremediation of lead contaminated soils will have both functions in landscape amenity and soil remediation.The six species of turfgrasses in this study was Lolium perenne, Festuca arundinacea, Agrostis stolonifera, Zoysia matrella, Eremochloa ophiuroides, and Paspalum vaginatum. The characteristics and capacity of lead tolerance and accumulation in these turfgrass species were investigated and the species and varieties with potential application in soil remediation were selected for further investigation in determination of critical thresholds and impacts of pH value and EDTA on the lead accumulation and translocation in the plants. The major results are as follows:Lead tolerance and accumulation in turfgrass under pot experiment: Compared with the control, the visual quality of six turfgrass decreased significantly after Pb2+ treatment at 8d; except Paspalum vaginatum, the visual quality of other turfgrass species decreased significantly at 56d. Plant height decreased significantly except Paspalum vaginatum at 60d. Pb2+ treatment didn't have obvious effect on leaf chlorophyll contents and root dry weight, but shoot dry weight differed significantly among the species. Different species showed the different characteristics in lead accumulation and translocation. Pb2+ was absorbed and accumulated mainly in the root with minority transported to the shoot. Shoot lead content and translocation coefficient in Festuca arundinacea were the highest in six turfgrass, which were 6587.0ug/g and 0.32, respectively. The lowest was Paspalum vaginatum with 759.8ug/g and 0.06, respectively. According to the results, Lolium perenne, Festuca arundinacea, Agrostis stolonifera, Zoysia matrella and Eremochloa ophiuroides can be used for the phytoextraction of lead contaminated soil, and Festuca arundinacea is the best choice among them. The lead accumulation in Paspalum vaginatum was very low, but the lead tolerance was the best, so it can be used for phytostabilization of the high lead contaminated soils.The critical thresholds of soil lead tolerance of Eremochloa ophiuroides, Paspalum vaginatum and Festuca arundinacea were investigated under the pot study. The results showed that: growth of turfgrass was promoted by low Pb2+ concentrations (≤1500mg/kg) and inhibited under high Pb2+ concentrations (≥4000 mg/kg). After 56d of treatment, visual quality of Eremochloa ophiuroides, Paspalum vaginatum and Festuca arundinacea decreased significantly respectively when Pb2+ concentration reached over 4000mg/kg, 5500mg/kg, and 1500mg/kg. Chlorophyll contents, Fv/Fm and root dry weight were not significantly inhibited under different Pb2+ concentrations. Pb2+ content in shoot and root increased with increasing the treatment concentrations. According to the root tolerance index and root length, critical thresholds of soil lead tolerance of Festuca arundinacea, Eremochloa ophiuroides and Paspalum vaginatum were 1500mg/kg,2500ug/g, and 4000mg/kg, respectively.Effect of pH value on the lead accumulation of Lolium perenne and Festuca arundinacea was studied under hydroponic experiment. pH value did not showed significant effects on shoot and root dry weight of turfgrass, but pH significantly affected the lead accumulation. The greatest lead uptake in shoot and root of Festuca arundinacea was at pH 5, with 9956.4ug/g and 7962.3ug/g, respectively. The greatest lead uptake in shoot of Lolium perenne was at pH 4, and the root at pH 6, with 11215.8ug/g and 9417.7ug/g, respectively. At pH 4, translocation coefficients of Festuca arundinacea and Lolium perenne were the largest, which were 1.30 and 1.48, respectively. Effect of EDTA on lead accumulation of turfgrasses: EDTA treatment had no significant effect on the growth of Festuca arundinacea and Paspalum vaginatum , but significantly inhibited the growth of Eremochloa ophiuroides. EDTA significantly increased the lead content in shoot and root of turfgrasses. Among them, EDTA promoted best in Festuca arundinacea and the worst in Eremochloa ophiuroides. Lead content in shoot and root of Festuca arundinacea increased to 14046.8ug/g and 31207.2ug/g, which were 2.13 and 1.53 times compared to control. At the same time, EDTA improved translocation coefficient of Festuca arundinacea, translocation coefficients added to 0.45 compared to CK (0.32). But EDTA had nearly no effect on the translocation coefficients of Paspalum vaginatum and chloa ophiuroides.