硅调控复合污染稻田水稻根际微域镉砷迁移的机制

Complex pollution of cadmium (Cd) and arsenic (As) becomes more serious in paddy soil in South of China, and as a result, concentrations of Cd and As in brown rice beyond the requirements of National Food Standards (GB 2762-2017) are of great concerns. There are many studies on remediation technology for single pollution, while the studies were limited to remedy the paddy soil complexly polluted with Cd and As. Silicon (Si) can reduce the concentrations of Cd and inorganic As in brown rice, but the transformation process, coupling relationship and mechanism of Si-Cd-As in different rhizosphere microdomains of rice are still unclear. In order to, this project takes the rice field system complexly polluted with Cd and As in area of Changsha-Zhuzhou-Xiangtan Hunan Province as the research subject. Phytogenic Si (RHA) was prepared from rice husk, and soil ripening tests, rice pot experiments and field experiments will be carried out, supplemented by RHA structure characterization and adsorption-desorption test. The contents of this project include: (1) to investigate the environmental behaviors of Cd and As in four rhizosphere microdomains of rice (soil, pore water, microorganisms and iron plaque) treated with RHA; (2) to study the effects of Si on the uptake and accumulation of Cd and As in the rice field system and in the different growth stages of the rice; and (3) to reveal mechanisms of environmental chemical behaviors of Cd and As migration and transformation in rice field system regulated by Si. The completion of this project will provide a theoretical basis for remediation of rice field system complexly polluted with Cd and As and rice safe production.

我国南方稻田土壤镉砷复合污染问题严重，糙米镉砷超标问题倍受关注。目前单一污染阻控技术研究较多，同时阻控复合污染稻田系统镉砷迁移的研究有限。外源施硅可降低稻米镉砷累积，但硅-镉-砷三者在水稻根际不同微域中行为转化的过程、三者的耦合作用关系及不同微域间的联动机制仍需探索。为探明这一科学问题，本项目以湖南长株潭地区镉砷复合污染稻田系统为研究对象，利用谷壳制备植源性硅，开展土壤培养试验、水稻盆栽试验和大田试验，并辅以植源性硅结构表征、吸附-解吸试验，研究土壤溶液、根际土壤、根际微生物和根表铁膜4个根际微域中硅对镉砷生物有效性、赋存形态、结合方式等环境化学行为的作用过程，硅-镉-砷三者在4个微域中的联动过程，土壤-水稻系统中镉砷迁移转运的作用过程，以及水稻不同生育期镉砷吸收累积效应，揭示硅调控水稻根际微域镉砷迁移的环境化学行为，减少水稻镉砷累积的机制，为利用硅修复治理镉砷污染稻田提供新的理论基础。

我国南方稻田土壤镉砷复合污染问题严重，硅在缓解土壤镉砷危害，降低糙米镉砷含量上起着重要的作用。项目以湖南长株潭地区镉砷复合污染稻田系统为研究对象，利用谷壳制备植源性硅（RHA），系统阐述了硅调控水稻根际微域镉砷迁移的环境化学行为减少水稻镉砷累积的机制，发表论文5篇，其中SCI论文2篇，以第一完成人授权发明专利1项，培养硕士研究生3名。主要结果如下：RHA通过提供活性硅，改变土壤镉的赋存形态，0.5-2%RHA的施用可使土壤有效硅含量显著增大26.4%–38.6%，镉的残渣态占比则由15.9%上升到22.1%，降低其可溶态含量（0.9%–5.6%），从而降低其在根表铁膜（8.7%-28.8%）、水稻根（34.2%–68.8%）、茎（61.1%–83.8%）和水稻糙米（36.8%-75.4%）中的镉的含量。而对于砷，RHA是通过改善土壤物化环境，土壤有效态砷可降低11.1%–47.1%，使得水稻根系生长茂盛，根表铁膜量增大（9.4%–53.7%），铁膜砷含量也增大（28.0%–33.1%），但铁膜向根系、根系向茎的砷转运系数则分别从2.672、0.317降低到1.288、0.166，减少水稻根系对砷的吸收，降低了14.9%–38.1%，进而水稻糙米砷含量可最大降低30.8%。RHA的施用有利于土壤厚壁菌门、拟杆菌门和粘液菌门等门水平物种的相对丰度增加，而绿弯菌门和芽单胞菌门等门水平物种的相对丰度降低，促进红细胞菌属、厌氧粘细菌属、氢化菌属、链霉菌属、诺卡氏菌科、丛毛单胞菌属等微生物生长。同时，RHA的施用增强了水稻根际土壤脲酶、蔗糖酶和酸性磷酸酶和脱氢酶活性，分别增强0.1%~9.4%、1.5%~22.6%、0.2%~24.5%和6.7%~224.1%，有效增加土壤中参与C、N、P循环的功能微生物数量，从而有利于水稻茂盛生长。