1.Institute of Subtropical Agriculture, Chinese Academy of Sciences;2.College of Agronomy, Yangtze University
Supported by National Natural Science Foundation(No.41807145), Hunan Innovative Province Construction Special Fund Project (No.2020NK2001), the Earmarked Fund for China Agriculture Research System（No.CARS-16-E09）
通过盆栽试验，在水稻分蘖盛期土壤水分落干过程的第0、3、5、7 d进行连续性取样，研究干湿交替的落干（“氧化”）过程中镉、砷在土壤-水稻系统中的迁移转化动态规律。结果表明：落干过程中水稻各部位镉含量随着落干天数的延长而增加，落干后第5 d水稻根内和茎叶镉含量较落干0 d处理分别提高了109%和183%（P<0.05）；而水稻根内砷含量随着落干天数的延长先减少后增加，与落干0 d处理相比，落干后第3 d减少了41.96 mg·kg-1（P<0.05）；茎叶砷含量则随着落干天数的延长而降低，落干后第5 d和第7 d茎叶砷含量较落干0 d处理分别减少了12%和18%（P<0.05）。落干后第5 d处理根表铁膜镉、砷和铁含量分别较无明水提高了97%、16%和16%（P<0.05）。随着土壤含水量的降低，土壤Eh逐渐升高、 pH逐渐降低、土壤可溶性有机碳增高和有效铁含量降低，促进了土壤中残渣态镉向酸提取态和可还原态镉转化，有效态镉（DTPA法）含量升高，土壤中砷向可氧化态转化，降低有效砷的含量。通过拟合分析可知，当土壤含水率为33.6%左右时，生物可利用的镉和砷含量可同步保持在相对较低水平。综上，对于镉砷复合污染土壤可采取适当的水分管理，通过调控土壤Eh、pH、DOC和有效铁，降低土壤镉砷生物有效性，促进根表铁膜对镉砷的吸附固定，进而减少水稻对镉砷的吸收累积，对重金属镉砷复合污染土壤的修复与治理具有重要意义。
【Objective】The chemical behavior of cadmium (Cd) and arsenic (As) in paddy soils is opposite to the change in biological efficiency. This presents serious challenges to the simultaneous control of Cd and As pollution in rice. Previous studies have found that continuous flooding of Cd polluted fields can reduce the bioavailability of Cd while reducing soil water content can mitigate the bioavailability of As. However, the forms and availability of Cd and As in the soil-rice system under the process of drying (oxidation) remain unclear. 【Method】In this study, continuous sampling during the process of drying (days 0, 3, 5, and 7 of the drying process) under tillering period of rice in a pot experiment was carried out. At the same time the soil samples were analyzed for pH, Eh, soluble organic carbon, available Cd and As, and the different forms of Cd and As. Also, the plant samples were analyzed for Fe plaque in the rice roots and Cd and As concentration in the rice tissues. 【Result】 The results showed that: during the process of drying, the Cd concentration in all parts of rice tissues increased with a reduction in water content, and the Cd concentrations in roots and shoots were increased by 109% and 183%, respectively, under the second drying stage (drying for 5 days) compared with the control treatment (P < 0.05). The concentration of As in rice roots decreased firstly and then increased with the reduction of water content. Compared with the control treatment, the concentration of As in rice roots was decreased by 41.96 mg·kg-1 (P < 0.05). Also, the shoot As concentration was decreased by 12% and 18%, respectively, under the second and third stages of drying (drying for 5 and 7 days) (P < 0.05). The Cd, As and Fe concentrations in the Fe plaque increased by 96%, 16% and 16%, respectively (P < 0.05). With the decrease of soil water content, soil Eh, soil soluble organic carbon, and soil available Cd extracted by DTPA were increased, but soil pH, soil available As, and soil available Fe extracted by DTPA were decreased. In addition, reducing soil water content promoted the transformation of residual Cd to acid extractable and reducible Cd, resulting in the increase of oxidizable As concentration. It was also observed that when the soil moisture content was 33.6%, the bioavailable Cd and As concentration remained relatively low. 【Conclusion】Reasonable water management practices can reduce the bioavailability of Cd and As in soil. This is due to the changing soil Eh, pH, soluble organic carbon and available Fe, and the promotion of adsorption and fixation of Cd and As by the Fe plaque. However, it is worth noting that while exploring water management methods to reduce the bioavailability of Cd and As, the growth and development of rice cannot be ignored. Our study contributes to the wealth of knowledge aimed at improving the remediation of Cd and As contaminated soils.
zhangyuting,朱奇宏,huangdaoyou, tianyingbing, xuchao, zhuhanhua, helei, wangwei, zhangquan. Effects of drying and oxidation stage on the forms and availability of Cd and As in the soil-rice system[J]. Acta Pedologica Sinica,,[In Press]