| With the advance of industrialization of human society,pollutants containing heavy metals have constantly entered the environment.Because of degradation-resistant,high toxicity and easy accumulation through food chains,heavy metals pose a great threat to human health and social development.Heavy metal concentrations in vegetable field are generally higher than those in grain field and the ability of vegetable to accumulate heavy metals is strong.Therefore,heavy metal pollution in vegetable filed(such as Pb,Cd,Cu and Zn)is a matter of particular concern.Facing the challenge of decreasing effective cultivated land area and increasing heavy metal polluted area,seeking effective ways to reduce heavy metal concentrations in vegetable is significant to ensure the quality and safety of vegetable and to promote sustainable development of agriculture.Existing studies found that biochar is rich in phosphorus,potassium and other nutrients,alkaline,aromatic and has high specific surface area and high porosity.Because of special properties,biochar has high agricultural value and great potential in environmental remediation.At present,research concerned with biochar has mainly focused on carbon dioxide fixation and biochar application in agricultural production.However,few researches were concerned with the effect of biochar application on bioavailability of heavy metals in soil and accumulation of heavy metals in vegetable.In order to investigate environmental effect of biochar application on heavy metal polluted soil and the effect of biochar application on accumulation of heavy metals in vegetable and vegetable quality,this study chose two widely eaten vegetables,namely leaf vegetable and root vegetable,as vegetable species and rice husk biochar(RHB)as research object.This study mainly focused on:(1)accumulation charateristics of different vegetables and those of different tissues in the same vegetable in Cd-polluted soil or Pb,Cd,Cu,Zn-polluted soil,and the effect of Cd on the growth of vegetable and mineral nutrients concentrations in vegetable;(2)the effect of biochar application on bioavailability of heavy metals in Pb,Cd,Cu,Zn-polluted soil;(3)the effect of biochar application on heavy metal concentrations in edible parts of vegetables in Pb,Cd,Cu,Zn-polluted soil;(4)theeffect of biochar application on the growth of different vegetables and their nutritional quality.Main conclusions are as follows:(1)In Cd-polluted soil,Cd was mainly distributed in edible parts of vegetables and inhibited the growth of edible parts of vegetables.As for carrot biomass,there was a hormesis effect of Cd on the growth of carrot.The biomass of under-ground parts and above-ground parts of carrot reached the highest value under low-dose Cd treatment(3ug·g-1),however,thatof under-ground parts and above-ground parts of carrot decreased significantly under high-dose Cd treatment(9ug·g-1).As for lettuce biomass,high-dose Cd treatment(9ug·g-1)inhibited the growth of lettuce.The biomass of under-ground parts and above-ground parts of lettuce reached the lowest value under high-dose Cd treatment(3ug·g-1).In Cd-polluted soil,Cd concentrations in leaf vegetable and root vegetable were correlated positively with mineral nutrient concentrations in leaf vegetable and root vegetable.In Pb,Cd,Cu,Zn-polluted soil,different tissues of vegetable varied in the ability to absorb heavy metals.Pb,Cd,Cu,Zn concentrations in under-ground parts of lettuce were higher than thosein above-ground parts of lettuce;Cd and Zn concentrations in above-ground parts of radish were higher those in under-groundparts;and Pb concentrations in under-ground parts of radish were higher those in above-ground parts.And there is no regularity in the distribution of Cu in radish.As for Cd,Pb,Cu,adsorptive ability of leaf vegetable was better than root vegetable.As for different heavy metals,adsorptive ability of lettuce wasCd>Cu>Zn>Pb,and adsorptive ability of radish was Cd>Zn>Cu>Pb.(2)In Pb,Cd,Cu,Zn-polluted soil,biochar application with 1%RHB,2%RHB and 5% RHB application rate could reduce soil pH and increase Dissolved Organic Carbon(DOC)concentrations.Biochar application could increase EC in lettuce soil,however,it had no influence on EC in radish soil.In muti-metal polluted soil,biochar application could increase bioavailable Cd and Zn concentrations in soil,and had no significantinfluence on bioavailable Cu concentrations in soil.And the effect of biochar application on bioavailable Pb concentrations in soil depended on biochar application rate.Low-dose biochar application(1%RHB)could increase bioavailable Pb concentrations in soil;moderate-dose biochar application(2%RHB)had no significantinfluence onbioavailable Pb concentrations in soil;high-dose biochar application(5%RHB)could decrease bioavailable Pb concentrations in soil.Bioavailable Cd and Zn concentrations in soil were significantly or extremely significantly negatively correlated with soil pH.(3)In Pb,Cd,Cu,Zn-polluted soil,biochar application with 1%RHB,2%RHB and 5% RHB application rate could significantly increase Cd,Zn and Pb concentrations in edible parts of lettuce,however,it had no significant influence on Cu concentration in edible parts of lettuce;biochar application had no significant influence on Cd concentration in edible parts of radish,high-dosebiochar application(5%RHB)could significantly increased Zn concentration in edible parts of radish,and moderate-dose biochar application(2%RHB)could significantly decreased Pb,Cu,Zn concentrations in edible parts of radish.Cd and Zn concentrations in edible parts of vegetables were significantly or extremely significantly positively correlated with soil pH.(4)In Pb,Cd,Cu,Zn-polluted soil,biochar application could promote the growth of different vegetables and improve their nutritional quality.With biochar application rate increasing,biomass of above-ground and under-ground parts of vegetables also increased.As for nutritional quality of vegetable,biochar application with 1%RHB,2%RHB and 5% RHB application rate could significantly increase nitrate concentrations and Vc concentrations in radish,whereas it could significantly decrease reducing sugars concentrations in radish.In addition,low-dose(1%RHB)and moderate-dose biochar application(2%RHB)could significantly increase amino acid concentrations in radish,whereas high-dose biochar application(5%RHB)had no significant influence on amino acid concentrations in radish.As for lettuce,biochar application had no significant influence on reducing sugars concentrations in lettuce,however,low-dose(1%RHB)and high-dose biochar application(5%RHB)could increase amino acid concentrations in lettuce,and high-dose biochar application(5%RHB)significantly increased nitrate concentrations and Vc concentrations in lettuce.In addition,biochar application could facilitate the absorption and utilization of most mineral nutrients in vegetables.More specifically,biochar application could facilitate the absorption of P,K,Mn,Ni in different tissues of radish as well as the absorption of Fe in radish shoot and total radish,however,it could inhibit the absorption of Fe and Mg in radish root;biochar application could facilitate the absorption of P and Kin different tissues of lettuce,whereas it could inhibit the absorption of Fe in lettuce root and total lettuce.And there was a hormesis effect of biochar application on Mn and Ni concentrations in lettuce root and total lettuce.Low-dose biochar(1%RHB)could increase Mn and Ni concentrations in lettuce root and total lettuce,however,high-dose biochar(5%RHB)could decrease Mn and Ni concentrations in lettuce root and total lettuce. |
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