The Regulation Of Chelating Agents And KH₂PO₄ On Cadmium Chemical Forms And Accumulation In Tall Fescue

Cadmium?Cd?pollution is one of the serious environmental problems for human healthy.Phytoremediation is a safe and cost effective method to clean up Cd-contaminated soils.The efficiency of phytoremediation was affected by Cd translocation in plants and their biomass.Fertilizers and chelating agents were among the regulating factors in phytoremediation.This paper focus on the regulations of foliar phosphorus and chelating agents on cadmium distribution and transportation in leaves of tall fescue,and the process of Cd secreted out of tall fescue leaf surface was also observed.The main results were:?1?There were significant difference between the effects of foliar and root phosphorus treatments on the Cd chemical forms deposited in leaves and the further effects on the Cd translocation from root to shoot.The foliar phosphorus increased Cd concentration and total Cd deposit amount in leaves as well as in whole plants,compared to the root phosphorus.The water-soluble organic acid complexes and the pectate-and protein-integrated Cd were the two major Cd chemical forms deposited in leaves.The foliar phosphorus treatment encouraged the Cd accumulated in the pectate-and protein-integrated forms.The results indicated that the foliar phosphorus enhanced Cd accumulation in leaves of tall fescue was associated with the detoxification mechanism to form the pectate-and protein-integrated Cd.?2?There were significant difference among 4 chelating agents?EDTA?DTPA?EGTA and citric acid?in regulation of Cd chemical forms and transportation in leaves.All chelating agents increased the percentage of water-soluble Cd and the increasing rate were EDTA?93.0%?,DTPA?81.4%?,EGTA?88.4%?,and Citric acid?38.4%?,respectively.Chelating agents enhanced the Cd translocation from roots to shoots,and the translocation factor were EDTA?1.26?,DTPA?0.63?,EGTA?0.43?,compared to 0.39 of the control.Chelating agents also enhanced Cd accumulation in the dead leaves and the Cd concentration increase in the dead leaves were EDTA?140.1%?,DTPA?54.3%?,EGTA?32.8%?,respectively.Our results indicated that EDTA had the strongest regulating effects on Cd translocation in tall fescue plant and the enhancement of cheating agents on Cd accumulation in dead leaves could be related to the increase of water soluble Cd form in tall fescue leaves.?3?The contrary results were found between foliar applications of citric acid and KH₂PO₄ on the Cd chemical forms and translocation in tall fescue.Foliar KH₂PO₄ increased leaf Cd concentration and the pectate-and protein-integrated Cd increased by 27.9%.Foliar citric acid decreased leaf Cd concentration and the water soluble Cd decreased by 23.2%and the pectate-and protein-integrated Cd decreased by 22.0%.When compared with the foliar citric acid,simultaneous application of KH₂PO₄and citric acid increased shoot Cd concentration by 21.3%,and the pectate-and protein-integrated Cd increased by 27.7%.When compared with the foliar KH₂PO₄,simultaneous application decreased shoot Cd concentration by 16.3%,and the pectate-and protein-integrated Cd decreased by 21.1%.The results indicated that the above regulations could be involved in Cd mobility.?4?The Cd secretion by tall fescue leaf was observed by fluorescence under Laser scanning confocal microscope.The surface of tall fescue leaf gradually accumulated Cd with the time of Cd treatment.No secretion of Cd from stoma was found,indicating that the stoma is not the channel of Cd secretion in tall fescue.The Cd fluorescence was mainly found on the opex and setae of tall fescue leaf and the strengthen of fluorescence overtime indicate the secretion of Cd may be related to hydathodes in tall fescue leaf.