| As one of the important natural resources in the ecosystem,soil is the basis for the sustainable development of human agriculture,not only because it is an important part of the terrestrial ecosystem,but also the most basic means of production and the basis for sustainable agricultural development.However,with the development of industry,agriculture and urbanization,the contamination of heavy metals in farmland soil has become very severe,where the contamination of cadmium（Cd）is particularly prominent.Therefore,how to control and remediate Cd-contaminated farmland and ensure the safety of food consumption and supply has become a hot spot in the remediation of heavy metal contamination in farmland soil.This research takes a Cd-contaminated farmland in southern Jiangsu as the research object,and carried out a two-year remediation experiment.For mild-moderate Cd-contaminated areas,single and combined remediation technologies such as in-situ passivation remediation,agronomic regulation,and low-accumulation varieties screening were used.For serious Cd-contaminated areas,plant growth regulators were used to enhance the absorption effect of Solanum nigrum L on Cd.The main findings of the research are as follows:（1）Research on the remediation of mild-moderate Cd-contaminated farmlandIn situ passivation test,three kinds of passivators,calcium magnesium phosphate fertilizer（CMP）,calcium chloroaluminate（TL）and attapulgite（AT）were selected for the test.Different types of passivators could increase soil pH and wheat yield after passivation twice,while reducing available Cd in soil and Cd content in wheat grain,but the increase and decrease effects after the second application were different from the first application.In terms of improving soil pH and wheat yield,the effect of the second application was lower than that of the first application.Specifically,the treatment of CMP 1500 kg/hm2（CMP-1500）had the greatest increase in soil pH,which increased by 0.97 units,and pH was 7.17;after CMP-1500 accumulation ability of Cd,and thus it is generally suitable for local promotion and cultivation after safe utilization measures.The results of the combined remediation technology in two seasons show that the treatment of attapulgite 6000 kg/hm2+ fertilizer substrate 3750 kg/hm2（ZH 2）was slightly more effective than CMP 1500 kg/hm2+fertilizer substrate 3000 kg/hm2（ZH 1）in terms of improving soil pH and yield and reducing Cd content in wheat grains.After ZH 2 treatment,pH was increased by 0.53,and pH was 6.76;ZH 2 treatment increased wheat yield by 6.2%,and the yield was 5633 kg/hm2;in terms of reducing the available C d content in soil,ZH 1 and ZH 2 decreased by similar magnitudes,being 48.3%and 48.1%,respectively;the Cd content in wheat grains ZH 2 and ZH 1 was reduced by 63.5%and 68.4%respectively compared with the one-time treatment,and the Cd content was 0.048 mg/kg and 0.045 mg/kg,meeting the specified limit（0.10 mg/kg）of grains in the Food Safety National Standard for Maximum Levels of Contaminants in Food（GB 2762-2017）.（2）Research on the remediation of serious Cd-contaminated farmland:The remediation of Cd-contaminated soil by Solanum nigrum L shows that the total biomass of Solanum nigrum L decreased with the increase of IDSA concentration after the single application of chelating agent IDSA,while the application of 28-epihomobrassinolide（TJ）could reduce the decreasing trend in the total biomass of Solanum nigrum;the application of IDSA changed the form distribution of Cd in the soil,with the content of weak acid state and reducible Cd increasing significantly,and with the increase of IDS A concentration,the total amount of bioavailable Cd enriched and absorbed by Solanum nigrum L increased;the combined application of 5 mmol/L IDSA and 28-epicomobrassinolide（IDSA-5+TJ）both improved the Cd BCF and transfer factor（TF）of Solanum nigrum,increased by 42.0%and 5.1%respectively compared with the control and the annual extraction of Cd from Solanum nigrum L increased by 34.1%compared with CK;at the same time,the activities of catalase,urease and sucrase in the soil of the combined treatment were better than those of the single application of chelating agent,ensuring that the soil after phytoremediation has agricultural production functions.Single application of chelating agent IDSA increased the content of malondialdehyde（MDA）in the leaves of Solanum nigrum,decreased the activities of catalase（CAT）and superoxide dismutase（SOD）,and increased the anti-oxidative stress effect of Solanum nigrum.The application of TJ could alleviate the oxidative stress of Solanum nigrum.Compared with CK,after IDSA-5+TJ treatment,the MDA content in Solanum nigrum L left only increased by 3.4%.CAT decreased by only 3.0%,while the peroxidase（POD）and SOD activities increased by 18.0%and 35.0%.respectively.The anti-oxidative stress ability of Solanum nigrum L was enhanced.At the same time,the determination of the root activity of Solanum nigrum L and the slice structure show that the addition of the chelating agent changed the distribution of Cd in the weak acid state,oxidizable state,reducible state and residue state in the soil.which enhanced the poisoning effect on the roots of Solanum nigrum L and the development of root tissue.Further,the root vitality decreased,and root’s absorption capacity of water and nutrients decreased,which affected the accumulation and transfer capacity of Solanum nigrum L for Cd.Fortunately,plant growth regulators could effectively alleviate the damage brought by the single application of chelating agent to the root cells and tissues of Solanum nigrum. |
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