巯基化凹凸棒石对水稻土中镉钝化效应的动态变化特征

Dynamic characteristic of the immobilization effect of thiolated attapulgite on cadmium in paddy soil

为了探究巯基化凹凸棒石作为钝化剂在土壤-水稻体系中对镉的钝化效应的动态特征规律,选取湖南和四川典型镉污染水稻土,分别以两个品种水稻为模式作物开展盆栽试验,在水稻生育期代表性阶段开展土壤-植物协同采样,并结合土壤培养实验,重点关注土壤理化性质和水稻各组织镉含量变化.研究发现,巯基化凹凸棒石以剂量1 mg·kg^(-1)和2 mg·kg^(-1)施用后,水稻分蘖期根茎叶镉含量明显降低40%以上,土壤有效态镉含量减少35.80%~55.08%.该快速显著的钝化效应,在水稻扬花期和成熟期维持稳定,收获时糙米镉含量最大降幅分别为76.65%和64.67%.巯基化凹凸棒石对土壤有效态镉的钝化过程符合二级动力学方程,钝化速率较快,高剂量组3 d可达到反应平衡.巯基化凹凸棒石对土壤pH无明显影响,可略微提高土壤氧化还原电位,增加土壤总硫和有效态硫含量,同时提升分蘖期水稻根系与根系表面铁和硫元素含量,降低分蘖期水稻根系对镉的生物富集系数和从根向茎的转运系数.综合土壤有效态镉含量和水稻吸收累积镉含量这两个核心因素,巯基化凹凸棒石在水稻-土壤体系中对镉具有快速且稳定的钝化效应.

To explore the dynamic characteristics of thiolated attapulgite(TA), an immobilization amendment in soil-rice system, typical cadmium(Cd) contaminated paddy soils in Hunan and Sichuan provinces were selected to conduct pot experiments with two rice varieties as model crops. Soil-plant collaborative sampling and soil culture experiments were carried out at the representative stage of growth period, primarily aiming to understand the dynamic changes in the physical and chemical properties of soils and Cd concentrations in various tissues of rice plant affected by TA. The results showed that the Cd concentrations in the root, stem, and leaf of rice in tillering stage decreased by more than 40% and the available Cd in soil decreased by 35.80%~55.08% after TA is applied at the dosages of 1 mg·kg^(-1) and 2 mg·kg^(-1), respectively. Its rapid and significant immobilization effect was stable at heading stage and maturity stage. The maximum reduction of Cd in grains were 76.65% and 64.67%, respectively. The immobilization process of TA on available Cd in the soil can be interpreted with the second-order kinetic equation with fast immobilization rate. The reaction equilibrium was reached in 3 days in the high-dose group. TA had no significant effect on soil pH in each collaborative sampling period, but slightly increased soil redox potentials. Additionally, it increased the soil total sulfur and available sulfur concentrations, enriched the iron and sulfur concentrations in rice root and root surface at tillering stage, and reduced the bioconcentration factors of Cd in rice root and the transfer factors from root to stem. The formation of iron plaque on the surface of rice roots at the tillering stage inhibited the uptake of Cd by rice roots from soil and the transport of Cd to shoots. This research showed that TA had a rapid and lasting immobilization effect on Cd in rice-soil system.