Research On The Distribution And Accumulation Of Heavy Metal In Loquat Tree And Effects On Quality Of Loquat Fruits

This research was conducted by applying different concentrations of Cadmium chloride, lead nitrate, potassium dichromate and copper sulphate to soil around the adult bearing 'Dawuxing' loquat trees .The contents of Cd²⁺, Pb²⁺, Cr⁶⁺and Cu²⁺in roots, branches, leaves and fruits of loquat were, analyzed. The effects of heavy metals on main nutritional quality of loquat fruits, the distribution of Cd²⁺, Pb²⁺, Cr⁶⁺and Cu²⁺ in organs of loquat trees and the dynamic changes of accumulation in fruits were studied in this paper. It would provide theoretical basis for non-pollution and green loquat production by monitoring environmental index. The results showed as follows:1,Rules of distribution and transportationThe accumulations of Cd²⁺ and Cr⁶⁺ in roots, branches, leaves and fruits increased respectively with the increase of the concentration of Cd²⁺ (0.1-0.5mg/L) and Cr⁶⁺ (60-180mg/L) in soil, and the contents of Cd²⁺ and Cr⁶⁺ in different organs had significant difference (P<0.01) respectively among different concentrations. The contents of Pb²⁺ in roots, branches, leaves and fruits were positively related with the concentrations applied to soil within 10-90mg/L and the content of Pb²⁺ in the these organs had significant difference (P<0.05) among different concentrations. But contents in leaves and fruits had no significant difference compared with control treatment within 10-30mg/L. The contents of Cu²⁺ in roots, branches and leaves all increased with the increase of the concentration of Cu (20-100mg/L) in soil. The content of Cu in fruits increased with the increase of the concentration of Cu²⁺(20-60mg/L) in soil, but declined within 80-100mg/L.The contents of Cd²⁺, Pb²⁺ and Cu²⁺ in different organs of loquat was in the order of roots>branches>leaves>fruits. And the contents of Cd²⁺, Pb²⁺ and Cu²⁺ in different organs had significant difference (P<0.05). Roots accumulated the highest content of Cr⁶⁺. The content of Cr⁶⁺ in roots had significant difference (P<0.01) with branches, leaves and fruits respectively, but the contents in branches and leaves had no significant difference (P>0.05). The order of Cr⁶⁺ contents in different organs of loquat was roots>branches (leaves)>fruits.The ratio of Cd²⁺, Pb²⁺, Cr⁶⁺ and Cu²⁺ contents in underground part of loquat to total content in all organs increased with the increase of the concentration of heavy metals in soil. The ratio of distribution of Cd²⁺, Pb²⁺, Cr⁶⁺ and Cu²⁺ in roots of loquat was in the order of Pb²⁺ > Cr⁶⁺(Cu²⁺) > Cd²⁺. The harm of Pb²⁺ to underground part of loquat was higher than other heavy metals, and the harm of Cd²⁺ to overground organs of loquat was the highest among the four heavy metals.2,Dynamic changes of Cd²⁺, Pb²⁺, Cr⁶⁺ and Cu²⁺in loquat fruitsCd²⁺ was quickly transported from soil to fruits after being applied to soil 30 days and the accumulation of Cd²⁺ in fruits reached the maximum (0.0203mg/kg) at 50 days. The peak time of Cd²⁺ absorption in fruits was in 30 to 40days after being applied to soil, from 0.0190mg/kg to 0.0201 mg/kg. Cu²⁺ was quickly transported from soil to fruits after being applied to soil 20 days. Cu²⁺ content in fruits rose slowly and reached the maximum (0.8461mg/kg) within 40 to 50 days after being applied to soil. The peak time of Cd²⁺ and Cu²⁺ accumulation in fruits was one month before loquat ripeness.The peak time of Pb absorption in fruits was in 30 to 60 days after being applied to soil, from 0.0824mg/kg to 0.1213mg/kg. The peak time of Cr⁶⁺ absorption in fruits was in 30 to 50 days after being applied to soil, from 0.1059mg/kg to 0.1809mg/kg. Pb²⁺ and Cr⁶⁺ accumulated in fruits reached the maximum at 20 days before loquat ripeness, 0.1213 mg/kg and 0.1857 mg/kg respectively.3,Effects of different concentrations of Cd²⁺, Pb²⁺, Cr⁶⁺ and Cu²⁺on main nutrition quality of loquat fruitWithin the concentrations of the treatments, soluble sugar content increased under Cd²⁺ with the increase of the concentrations of the heavy metals in soils. Soluble sugar content increased firstly and then declined under Pb²⁺, Cr⁶⁺ and Cu²⁺ treatments. Titratable acid content had a tendency of decreasing under the treatments of Cd²⁺,Pb²⁺,Cr⁶⁺ and Cu²⁺. Ascorbic acid content of loquat fruit decreased with the increase of the concentrations of Cd²⁺ and Pb²⁺ in soil, within the concentrations of Cd²⁺ (0.1-0.5mg/L) and Pb²⁺(60-180mg/L). Ascorbic acid content increased when Cr⁶⁺concentration was in 60-120mg/L and Cu²⁺ concentration was in 20-60mg/L, and declined when Cr⁶⁺ concentration was in 120-180mg/L and Cu²⁺ in 60-100mg/L. Soluble protein content of loquat fruit increased slowly with the increase of Cd²⁺ (0.1-0.5mg/L). Soluble protein content increased under low concentration (10-50mg/L) and decreased significantly under high concentration (50-90mg/L) by Pb²⁺ treatments. Under Cr⁶⁺ treatments (60-180mg/L), soluble protein content declined. Soluble protein content increased under low concentration of Cu²⁺ (20-60mg/L) and declined under high concentration (80-100mg/L).4,Comparison contents of Cd²⁺,Pb²⁺,Cr⁶⁺and Cu²⁺ in loquat fruit with the maximum limits of heavy metals in non-contaminated loquatUnder the treatments of highest concentrations of Cd²⁺,Pb²⁺,Cr⁶⁺ and Cu²⁺ , the contents of the four heavy metals in soil were all excess of the limited value of heavy metals in soil of quality standard for non-environmental pollution fruit place of product.Under all the treatments in this experiment, the maximum content of Cd²⁺,Pb²⁺,Cr⁶⁺ and Cu²⁺ in loquat fruit was 0.0203mg/kg, 0.1213mg/kg, 0.1857mg/kg and 0.7005mg/kg respectively , which were lower than the maximum limits of heavy metals in non-contaminated loquat(Cd²⁺≤0.03mg/kg; Pb²⁺≤0.2mg/kg; Cr⁶⁺≤0.5mg/kg ; Cu²⁺...