Effects Of Arbuscular Mycorrhizal Fungi On The Growth And Cadmium Uptake Of White Clover After Addition Of Organic Manure And Straw

Cadmium(Cd)is a heavy metal element.Soil Cd pollution was an important factor that can limit healthy and sustainable agriculture development in China.Addition of organic manure(OM)and straw to cadmium-contaminated soil can affect the absorption of nutrient elements and cadmium by plants.Arbuscular mycorrhizal fungi(AMF)were found to be beneficial microorganisms that widely existed in the soil.AMF inoculation could increase plant nutrient element uptake and reduce the toxicity of heavy metal elements to plants.However,there are still few studies on the impact of AMF and organic materials on plant yield,nutrient element uptake and Cd uptake in the soil contaminated with Cd.In this study,Cd-contaminated soil was selected as the tested soil and white clover(Trifolium repens L.)was selected as tested plant.There are two pot experiments in our study:Experiment 1.Effects of organic manure and AMF on yield and Cd absorption of T.repens in soil contaminated with Cd.This experiment included two soil treatments(sterilized soil and non-sterilized soil(natural soil)),three organic manure(OM)amendment levels(0%OM,2.5%OM and 5%OM,w/w)and two AMF inoculation treatments(non-AMF and AMF inoculation).The main results were as follows:(1)In treatments with AMF inoculation in the sterilized soil,the root mycorrhizal colonization of T.repens significantly decreased with the increasing of level of OM addition.In the non-sterilized soil,regardless of AMF,OM addition had no significant impact on mycorrhizal colonization.Compared with the treatments without AMF,AMF significantly increased the shoot and root biomass accumulation in the sterilized soil treated with 2.5%OM and 5%OM.Compared with the treatments without AMF,AMF inoculation had no significant impact on the shoot and root biomass of T.repens in the non-sterilized soil.In the two AMF treatments in the non-sterilized soil,compared with the treatments without OM addition,the shoot biomass was significantly increased by 2.5%OM addition,while the biomass was significantly decreased by 5%OM addition.(2)Regardless of whether AMF was inoculated and whether the soil was sterilized,compared with the treatments without OM addition,the nitrogen(N),phosphorus(P),potassium(K)and magnesium(Mg)concentrations of shoot and root tissues,as well as the Cd concentration of roots in T.repens were elevated by OM addition.In the soil after sterilization without AMF,the shoot and root contents of N,P,Ca and Mg and root contents of Cd in the plants treated with 2.5%OM were significantly higher than plants treated with 5%OM.In the soil without sterilization and inoculation,plants with 2.5%OM application had significantly higher shoot and root N,and P contents than plants grown in soils treated with 5%OM.It was found that OM addition significantly enhanced the available P concentration,pH value,microbial biomass N(MBN),dissolved organic carbon(DOC)and soil exchengeable Cd(DTPA-Cd)in the soils.Experiment 2:Effects of straw addition and AMF on the growth and Cd uptake of T.repens at different cadmium levels.This experiment included four Cd levels(0(Cd0),10(Cd10),20(Cd20),50(Cd50)mg Cd kg-1),two straw treatments(no straw and straw addition(+S)),and two AMF treatments(not inoculated with AMF and inoculated with AMF(+AMF)).The main results were as follows:(1)In the CdO,Cd10 and Cd20 treatment group,regardless of whether straw was added or not,compared with the treatments without AMF inoculation,AMF inoculation significantly enhanced the shoot biomass,root biomass and total biomass of T.repens.In the Cd50 treatment with straw addition,AMF inoculation had a promotional effect on the T.repens biomass.Compared with the non-straw addition treatments,straw addition had no impact on the T.repens biomass in the CdO,Cd10 and Cd20 treatments,but straw addition significantly decreased the shoot and root biomass of T.repens in the Cd50 treatment without AMF inoculation.(2)Regardless of whether straw was added,the P concentrations,P,K,Ca contents of shoot and root tissues,shoot Mg content at all cadmium levels,shoot Cd content in the Cd10 and Cd20 treatments,and root Cd content in the Cd20 and Cd50 treatments were significantly increased by AMF inoculation in comparison to non-inoculation treatments.In comparison to the non-inoculation treatments,AMF inoculation significantly decreased the shoot Cd concentration and translocation factor at both two straw treatments.AMF inoculation significantly decreased the soil available P concentration in comparison to the uninoculation treatments at all Cd levels.Compared with non-straw addition treatments,straw addition significantly decreased the soil available P concentration,and increased the activities of urease and acid phosphatase at all Cd levels.The research conclusions were as follows:(1)Both AMF inoculation and OM addition promoted the growth and nutrient element uptake of T.repens when soil was sterilized and contaminated with Cd.In the non-sterilized soil,it was observed that AMF inoculation had no impact on the growth and nutrient element uptake of T.2.5%OM addition promoted the plant biomass and nutrient element uptake of T.repens.(2)In the soil contaminated with Cd,AMF inoculation increased the biomass and nutrient element uptake of T.repens.In the 10 and 20 mg Cd kg-1 soils,AMF inoculation increased the shoot Cd content of T.repens,but straw addition did not change the biomass and nutrient element uptake of T.repens.In the 50 mg Cd kg-1 soils,AMF inoculation treatments significantly increased the biomass,nutrient and Cd element contents of T.repens in the straw addition treatments.