水稻秸秆来源生物炭施加后水稻根际亚铁氧化对三价锑氧化的影响

Oxidation of ferrous iron to its ferric form by Fe(II)-oxidizing bacteria (FeOB) would lead to precipitation of iron oxyhydroxides in the rhizosphere and on the root surface of wetland plants. Antimony (Sb) has a high binding affinity for iron oxyhydroxides, which would has an important effect on transition and bioavailability. The key problem in science of this project is, does ferrous iron oxidation mediate Sb(III) oxidation under microaerobic conditions in the rhizosphere of rice after supplement of biochar made by rice straw? (1)Simulation experiments will be conducted systematically to determine the species of antimony in the oxidation processes of Fe(II) by Fe(II)-oxidizing bacteria, antimony and iron concentrations, species of antimony and types of iron oxyhydroxides in iron plaque of rice roots of different gene types of rice, which are to ascertain the effect mechanism for oxidation of ferrous iron mediate Sb(III) oxidation by biochar made by rice straw; (2) Rhizobox experiments will be conducted with rice cultivars having different soils having different physicochemical properties such as pH, Fe and antinomy level, which are to ascertain the key environmental factors affecting Fe(II) oxidation coordinate Sb(III) oxidation and the key Fe(II) oxidizing bacteria flora after supplement of biochar made by rice straw; (3) Samples will be collected from the contaminated paddy field nearby an antimony mine after supplement of biochar made by rice straw and iron and antimony concentrations, speciations in iron plaques and rhizosphere soils will be analyzed, Fe(II) oxidizing bacteria in rhizosphere and bulk soils will be isolated and quantified, antimony concentrations in overground part of rice plant will be surveyed, and the key factors and bacteria affecting the antimony bioavailabilities in the rice's rhizosphere will be illustrated, which will provide scientific basis for revealing systematically and deeply the environmental effects of the oxidation process of the ferrous iron in the rhizosphere of rice and the wide use of biochar.

水稻根际亚铁氧化菌氧化亚铁形成氧化铁，氧化铁吸附锑，影响锑的迁移和生物有效性。生物炭影响土壤理化性质及锑的环境行为。施加水稻秸秆来源生物炭后水稻根际亚铁氧化菌氧化亚铁过程如何影响三价锑氧化为本课题的核心科学问题。本课题将模拟水稻根际微环境，采用水培实验研究生物炭对水稻根际铁与锑形态、根表铁膜氧化铁组成及锑形态、根表铁膜量与锑固定量及亚铁氧化菌群的影响，揭示生物炭对不同类型水稻根际亚铁氧化协同三价锑氧化的影响；采用根箱实验，以不同性质的土壤为对象，揭示生物炭存在条件下控制水稻根际亚铁氧化协同三价锑氧化的环境因子及亚铁氧化菌对环境条件的响应；以施加生物炭的锑污染稻田为对象，探讨关键生育期水稻根际土壤亚铁氧化影响三价锑氧化的关键微生物菌群及铁和锑形态变化与锑有效性的关系，揭示田间条件下控制土壤锑有效性的关键环境要素与微生物菌群，为探讨水稻根际亚铁氧化过程的环境效应及生物炭的广泛应用提供科学依据。

本研究以湖南冷水江锑矿区受锑污染的稻田土壤为研究对象，深入研究了生物炭对水稻根际微氧环境及土壤-水稻系统中锑(Sb)环境行为和过程的影响，主要结果包括：(1)水稻秸秆生物炭的组成及结构与制备温度密切相关，随着制备温度的升高有机碳组分含量升高、极性减弱、芳香性增强；(2)生物炭制备温度的升高和添加量的增加对氧气氧化亚铁及亚铁氧化菌氧化亚铁协同三价锑氧化等过程中铁与锑的形态有显著的影响；铁膜和基因型对锑在水稻体内的迁移和累积有显著影响；(3)向高锑污染的土壤中施加以水稻秸秆和稻壳为原料制备的不同类型生物炭后，土壤和孔隙水的基本理化性质及其中易迁移性锑的含量明显改变；生物炭的施加导致了土壤中残渣态Sb含量明显降低而其它形态的含量显著升高，铁铝氢氧化物结合态Sb仍占绝对优势，所以，生物炭的施加提高了土壤中Sb的迁移性和生物有效性；生物炭的添加显著促进了水稻根表铁膜的形成，提高了铁膜中铁的含量，但降低了铁膜对锑的固定量；生物炭的施加对水稻根茎生物量和根长没有显著影响，但提高了锑在水稻根/茎中的迁移效率，同时也有效促进了根际亚铁氧化菌群的生长，秸秆生物炭作用尤其明显；(4)向高锑污染的稻田土壤中施加不同量的硅，提高了不同基因型水稻根、茎、稻壳和谷粒的生物量，基因型差异明显；不同基因型水稻根表铁膜生产量及铁膜中铁/锑含量都有显著增加，而且籼稻比杂交稻高。杂交稻的根、茎、稻壳和谷粒中Sb的含量高于籼稻；硅的施加显著降低了水稻各器官内Sb的含量，且杂交稻的降低量要大于籼稻。水稻茎中占绝对优势的是Sb(III)，无机锑占总锑含量的90%以上；籼稻比杂交稻累积了更多的无机锑；硅的施加显著降低了无机锑的含量，而有机锑含量略有增加；(5)我国北方典型湖泊和河口湿地沉积物中锑的含量远高于环境背景值，铁铝氢氧化物结合态锑是其在沉积物中的主要存在形态，沉积物的矿物组成和有机质是影响锑环境行为的主要因素；对于远离锑矿开采和冶炼地区的锑污染问题应得到重视。