The Regulation Of Citric Acid And EDTA On Cadmium Accumulation In Tall Fescue And Kentucky Bluegrass

Cadmium（Cd）pollution has been posing a serious threat to human sustainable development.Phytoremediation is an environmental-friendly technology to alleviate heavy metals soil pollution,but its efficiency may be limited by plant concentration factor or translocation factor to some extent.Chelating agents can activate soil heavy metals so as to improve the capacity of accumulation or translocation in plants for better effects of phytoremediation.Preliminary studies on tall fescue（Festuca arundinacea）and Kentucky bluegrass（Poa pratensis）have shown high tolerance of Cd and high remediation potential in Cd-contaminated soil in both turfgrasses.By applying citric acid and EDTA,this paper mainly focused on the regulation mechanism of chelators on Cd concentration and translocation in two turfgrasses.The results are followed as below:（1）Tall fescue and Kentucky bluegrass showed significantly different responses in Cd uptake and accumulation.Under Cd treatment(100 mg Cd kg^-1),the concentrations of Cd in the root of tall fescue and Kentucky bluegrass were respectively 35.3 mg/kg and 66.9 mg/kg.Tall fescue had a higher Cd tolerance ability while with lower Cd translocation capacity,and these results may related to the function of F-NaCl,which is the dominant proportion of Cd in roots of tall fescue,in cell wall compartment;Under Cd treatment,the concentrations of Cd in the shoot of tall fescue and Kentucky bluegrass were respectively 17.6 mg/kg,53.2 mg/kg.With high proportion of F-ethanol and F-H₂O in its roots,Kentucky bluegrass had higher capacity of Cd translocation than tall fescue.This two turfgrasses showed different responses to citric acid in Cd uptake,translocation,and accumulation.Under CA treatment,Cd concentration in rhizosphere soil of tall fescue was significantly increased by 11.6 times,and the capacity of Cd uptake in tall fescue was also increased by 2.8 times,along with 3.0times of Cd accumulation increase in root and 2.3 times in shoot.The significant improvement of Cd uptake and translocation in tall fescue might be in relation to the increase of acid soluble Cd and organic acids in its rhizosphere;Under CA treatment,Cd concentration in rhizosphere soil of Kentucky bluegrass was increased by 2.8 times,and the capacity of Cd uptake in tall fescue was only increased by 1.2 times,along with 1.7 times of Cd accumulation increase in root while 30%decrease in shoot,which might be related to the decrease of amount of organic acids.（2）CA treatment significantly improved 1.8 times of Cd concentration of tall fescue in rhizodermis+cortex tissues,along with 1.5 times of promotion of F-NaCl in stele.Cd translocation might be promoted by the increase of Cd concentration in the stele of tall fescue.In Kentucky bluegrass,CA decreased the concentration of F-NaCl by 63%in rhizodermis+cortex and stele tissues,which might result in the reduction of Cd in its translocation.In tall fescue,CA significantly enhanced the concentration of F-HAc by 1.5 times in vascular bundle,while with the decrease of F-NaCl by 36%.Meanwhile,the concentrations of F-ethanol,F-H₂O and F-NaCl in epidermis+mesophyll tissues were also decreased by 52%.The decrease of the diffusion of Cd from its vascular bundle to the blades might be related to the low F-NaCl concentration in vascular bundle;In Kentucky bluegrass,CA treatment increased the concentration of F-HAc precipitated in its vascular bundle by 1.9 times,CA treatment also increased the concentration of all forms of Cd in its epidermis+mesophyll tissues.（3）Tall fescue and Kentucky bluegrass both showed positive response to EDTA in Cd uptake,accumulation and translocation.EDTA significantly promoted the capability of Cd uptake as well as long-distance translocation.In two turfgrasses,the proportions of soluble-state Cd in different tissues were enhanced while stable-state Cd was reduced,and concentrations of all forms of Cd were higher than that in control group in root tissues.In tall fescue,the concentrations of Cd in rhizodermis+cortex tissues and stele were respectively promoted by 2.1 times and 1.8 times.In Kentucky bluegrass,the concentrations of Cd in rhizodermis+cortex tissues and stele were respectively promoted by 2.5 times and 1.7 times.Under EDTA treatment,concentrations of almost all forms of Cd were higher than that in control group in shoot tissues of tall fescue and Kentucky bluegrass.In tall fescue,the concentrations of Cd in vascular bundle and epidermis+mesophyll were respectively increased by 2.7times and 1.5 times.In Kentucky bluegrass,the concentrations of Cd in vascular bundle and epidermis+mesophyll tissues were respectively increased by 2.2 times and 4.6 times.The above results suggested that EDTA promoted the uptake,translocation and accumulation of Cd mainly by increasing the content of water-soluble Cd in plants.