Effect And Mechanism Of Phosphorus And Iron Fertilizers Application On The Growth And Accumulation Of Copper By Castor(Ricinus Communis L.)

Castor?Ricinus communis L.?has been universally used for the remediation of copper?Cu?pollution of soil.It has the advantages of fast growth,high biomass,strong tolerance,and high harvest value.However,its accumulation ability for Cu needs to be improved.In this paper,the castor found in the Tonglv mountain bronze mine of Daye City,Hubei Province was regarded as the research object.The pot and hydroponic experiment were carried out to study the effect of phosphorus?P?and iron?Fe?fertilizers on the uptake of Cu by castor and its potential mechanism involved.This study is divided into three parts:?1?A pot experiment about application of Ca?H₂PO₄?₂?0,200,400 mg/kg?to study the effect of different application rates of P fertilizer on growth and uptake of Cu by castor;?2?A hydroponic experiment to study the potential mechanism of application of NaH₂PO₄?1.00,1.25,1.50 g/L?and Fe-EDTA?20,40,60 mg/L?fertilizers on growth and uptake of Cu buy castor;?3?A pot experiment to study the effect of Ca?H₂PO₄?₂ with Fe fertilizers,which included foliar Fe fertilizer?FeSO₄,50 mg/kg?and base Fe fertilizer?EDTA-Fe,20 mg/L?on growth and uptake of Cu by castor.The main results are as follows:?1?The pot experiment about application of P fertilizer indicates that,applying P fertilizer in heavy metal contaminated soil can promote the growth of castor,increase the concentration of Cu in castor,and inhibit the transportation of Cu from root to shoot.The total amount of Cu extraction by castor increased by 44.2%and 82.4%at P and 2P treatments,respectively,compared with the treatment without P fertilizer.Applying P fertilizer could lower soil pH,and decreased the contents of available Cu in the soil by3.1%-6.5%.After applying P fertilizer,the leaves showed chlorosis with yellow spots,and the Fe contents in castor decreased significantly.The available Fe contents in the soil decreased by 10.0%-11.7%.?2?The hydroponic experiment suggested that applying P fertilizer could increase the biomass and chlorophyll content of castor,increase root length,root surface area and root tip number,alleviate lipid peroxidation and reduce the degree of damage caused by Cu.The application of P fertilizer increased the content of malic acid and citric acid in the root exudates of castor by 1.2-1.3 times and 9.3-12.2 times.Moreover,application of P fertilizer could promote the transportation of Cu from root to shoot,increase the proportion of Cu in the root cortex and cell wall,enhance the proportion of cupric phosphate in the root,increase the content of ascorbic acid?AsA?and catalase?CAT?activity.?3?The application of Fe fertilizer promote the growth of castor and increase the chlorophyll content in leaves.Applying Fe fertilizer can reduced the Cu content in the roots of castor ranging from 3845.0-3961.9 mg/kg to 1714.2-2061.3 mg/kg,and the Cu content in the shoot decreased from 29.4-48.2 mg/kg to 9.4-29.3 mg/kg,the lower part of the root is lower than the shoot,so Fe fertilizer promote the transportation of Cu from root to shoot.The application of Fe fertilizer increased the content of low molecular weight organic acids in the root exudates of castor.Using SEM-EDS,it is found that the absorption of Fe and Cu in the roots of castor is completely opposite.Application of Fe fertilizer can reduce the content of hydroxyl and carboxyl groups in the root cell wall of castor,so enhance the fixation of Cu in root cell wall.The addition of Fe fertilizer reduced Malondialdehyde?MDA?content in castor,slowed lipid peroxidation in castor,and increased CAT activity.?4?Pot experiment about application of P and Fe fertilizers,indicated that foliar Fe fertilizer could significantly reduce the concentration of Cu in the shoot of castor,but enhance the concentration of Cu in the root of castor;Fe-based fertilizer could reduce the concentration of Cu in the root of castor.Application of 200 mg/kg P fertilizer combined with base Fe fertilizer and foliar Fe fertilizer could increase the total amount of Cu extracted from castor by 42.4%and 166.4%,respectively.The combination of high concentration P fertilizer with two Fe fertilizers can reduce the biomass of castor and reduce the accumulation of Cu.