富铁土氧化铁铝取代效应及其影响铁还原的生物化学机制

Ferrosols is a special soil orders in Chinese Soil Taxonomic Classification, and LAC-ferric horizon is its unique diagnostic horizon. Ferrosols contains a large amount of free iron oxides and is widely distributed in China, especially in tropical and subtropical zones. Al-substituted iron oxides is one of the most important feature under the effect of soil desilicification and allitization; the isomorphous substitution of Al for Fe in the iron oxide crystal structures may influence soil genesis, properties, the characteristics of microbial community, soil iron biogeochemical cycles as well as the transformation of contaminants in soils. This proposal will choose Ferrosols developing from different parent materials in South China as the research object, soil iron(III) reduction as the model reaction. Experiments are designed and conducted to investigate the biotic-abiotic mechanisms of iron(III) reduction in Ferrosols under the influence of Al-substituted iron oxides. The research tasks were detailed below: (1) to study the impact of Al-substitution effect on iron oxide crystal structures, surface properties, soil properties, to analyze the correlations between soil weathering degree and Al-substitution effect; (2) to investigate Al-substitution effect on soil iron(III) reduction, to study the relationship among soil iron(III) reduction, Al-substitution effect and soil weathering degree, and to reveal the chemical mechanisms of iron(III) reduction under the effect of Al-substituted iron oxides in Ferrosols; (3) using enrichment culture, high-throughtput sequencing technology and other microbiological research methods to study soil iron-reducing bacteria communities, to investigate the correlations between Al-substitution effect and soil iron-reducing bacteria communities, and to reveal the microbiology mechanisms of iron(III) reduction under Al-substitution effect in Ferrosols; (4) using statistical methods to analyze the relationship among soil iron(III) reduction, Al-substitution effect, soil properties, and soil iron-reducing bacteria communities, to disclose the biotic-abiotic mechanisms of soil iron(III) reducibility in Ferrosols under the Al-subsitution effect. Results of this proposal will improve our general understanding in soil pedogenesis and its biogeochemical impacts on typical elements' cycling processes; meanwhile, it will provide valuable information on soil iron redox chemistry as well as soil iron biogeochemical cycles researches.

富铁土纲分布广泛，富含游离氧化铁，脱硅富铁铝化成土过程中氧化铁晶格中的铁原子被铝取代，显著影响氧化铁结构与性质、土壤微生物群落结构，从而影响土壤铁循环等物质循环过程。本申请以华南不同母质发育的富铁土为研究对象，以铁还原为模型土壤过程，研究土壤氧化铁的铝取代效应对氧化铁晶体结构、表面性质、土壤理化性质的影响，探讨风化程度与氧化铁铝取代效应的关系；阐明土壤铁还原与铝取代效应、风化程度的关系，从而阐明铝取代效应影响土壤铁还原过程的化学机制。采用富集培养、高通量测序等技术，研究铝取代效应与土壤铁还原菌群落间的关系，阐明铝取代效应影响土壤铁还原过程的微生物学机制。采用数理统计方法深入分析土壤铁还原过程、铝取代效应与土壤理化性质、铁还原微生物群落间的关系，深入阐明铝取代效应影响土壤铁还原过程的生物化学机制。预期成果可为深入理解成土过程对土壤典型物质循环过程影响的生物地球化学机制提供科学依据。

本项目以氧化铁的铝取代效应影响铁还原的化学机制与微生物机制为核心科学问题，研究了铝取代效应对土壤铁还原过程的影响机制。研究结果表明：①铁氧化物中Al的存在会阻碍铁矿的晶相从磁赤铁矿向赤铁矿的转变，其比表面积随着Al取代率的升高以及烧结温度的降低而增加，阐明了Al取代铁氧化物中Al主要通过影响铁氧化物的晶体结构、结晶度和表面结构性能，从而进一步影响铁还原活性；②外源添加电子供体能显著提高铁还原速率，通过研究土壤中水溶性有机物(DOM)对活性Fe(II)还原2-NP过程的影响，揭示了低分子量有机酸的络合作用和高分子量有机酸的电子穿梭作用，阐明了DOM与活性Fe(II)协同促进2-NP还原转化的作用机制；③铁还原过程中土壤pH、酸提态（0.5 M HCl）铁、铝及硅的含量均发生改变；不同母质发育的水稻土铁还原速率沉积岩发育>玄武岩发育，不同土地利用方式的土壤铁还原速率水田＞水旱轮作＞林地；不同土地利用方式下土壤微生物群落差异显著，发现Acinetobacter细菌在PCP还原脱氯中重要作用，同时Fe(III)还原菌Clostridium在PCP还原转化中占优势，证实铁还原参与了土壤中PCP的还原转化过程；④选取祁阳红壤站长期定位观测试验中(1990~2013年间)不同施肥方式下的土壤样品为研究对象，研究发现不同施肥方式下土壤络合态铝形态含量与pH水提呈显著线性负相关关系，是土壤酸化过程中的活跃组分；定量分析表明伴随不同施肥方式下，次生氧化铁矿物中铝的取代率与土壤pH呈正相关关系，初步揭示氧化铁通过抑制活性致酸源铝的释放来控制土壤酸化的调控机制。今后可深入研究土壤氧化铁铝取代特性与关键元素地球化学循环过程的相互作用关系及机制。项目共发表SCI收录期刊论文6篇（第一标注3篇，第二标注2篇，第三标注1篇）；已投稿SCI研究论文3篇，审稿中（第一标注1篇，第二标注2篇）；参加国际学术会议2人次，国内学术会议6人次，口头报告7个，展板报告1次；协助课题组组长培养博士毕业生1名，独立指导硕士毕业生2名。