铁氧化微生物在湖泊沉积物磷转化过程中的地位与作用机理

The eutrophication of natural water bodies is determined by sedimental retention of endogenous phosphorus, which is mainly regulated by iron oxides in the sediments. Via radial oxygen loss, submerged macrophytes could promote iron oxide formation in the rhizosphere, thereby increasing the adsorption and immobilization of phosphorus in sediments. Microorganisms have been found to be involved, while it still remains unclear the mechanism of microbial iron oxidation in this process. The project aims to clarify this issue. The sediment samples will be taken from a eutrophic lake, followed by the determination of the physical and chemical characteristics, iron and phosphorus contents, as well as the microbial community structure and the abundance of iron cycle related bacteria. On the basis of that, a simulated lake experiment with collected water and sediments will be carried out to study the effects of changing environmental conditions on the formation and deposition of microbial iron oxides, as well as on phosphorus adsorption by the oxides. The significance of microbial-mediated iron oxides in sedimental phosphorus fixation will be further investigated by obtaining iron-oxidizing bacteria from sediments and inoculating them in the rhizosphere of Vallisneria natans in the simulated lake system. The accomplishment of this project is expected to reveal the combined effects of submerged macrophytes and iron oxidizing microorganisms on the controlling of phosphorus release from sediments and the key environmental factors, in order to provide reference for the recovery of eutrophic shallow water lakes.

沉积物对内源磷的滞留决定着自然水体的富营养化进程，而内源磷的固定与释放受到沉积物中铁的氧化物所调控。沉水植物可通过根系泌氧促进根际铁氧化物形成，从而增加对沉积物中磷的吸附固定。已发现微生物参与了这一过程,但其作用机理还不清楚，本项目拟围绕该问题进行研究。首先通过分析富营养化湖泊中受根系影响的沉积物的理化特性，铁、磷形态与含量,微生物群落结构特别是参与铁循环的微生物数量与种类,初步了解铁细菌在沉水植物根际固磷过程中的作用。在此基础上，采用底泥与湖水进行模拟培养试验，探讨环境条件改变对微生物参与的沉积物中铁氧化物的形成及对吸附固定磷素的影响。最后通过在沉水植物根际接种已知铁氧化功能菌的试验，进一步明确微生物介导的铁氧化物生成对沉积物中磷的吸附与固定的重要性。通过研究,阐明沉水植物与铁氧化微生物联合控制富营养化水体底泥磷释放的作用机理及该过程中的相关影响因素，为浅水富营养化湖泊治理提供参考依据。

铁氧化物从本质上决定着湖水富营养化的主要磷源（内源磷）的固定与释放。沉水植物通过根系沁氧，促进沉积物铁氧化物形成，进而吸附固定沉积物磷这一过程中的微生物的地位和作用机制尚不明确。.本项目选择泰州溱湖作为研究采样点。于不同季节，采集有沉水植物苦草生长与无植物生长区域的沉积物样品，分析测定沉积物基本理化性质及铁-磷、铝-磷等含量，湖泊沉积物微生物群落组成及相关环境因子。采集了湖泊沉积物，富集筛选具有氧化铁功能的细菌。对功能菌种或菌群进行鉴定，比较微生物氧化铁与化学氧化铁对溶液磷的吸附效应。建立了实验室模拟湖泊系统，比较苦草及铁氧化菌互作对铁氧化物生成及其对沉积物磷吸附的影响。.结果表明：1）苦草生长条件下，湖水的pH、氧化还原电位与溶解氧含量提高，最高为20.86%、67.13%、82.57%；沉积物的生物有效性铁、铁-磷含量增加，而有机质含量则有所下降。沉积物生物有效性铁五月最高，而铁磷与有机质含量最高则出现在九月。2）苦草生长影响沉积物细菌多样性，在春夏季生长旺盛期苦草区域细菌多样性高，而秋冬则低于无苦草对照区，尤其是一月份。沉积物细菌群落季节变化明显，有无苦草区域的细菌群落组成亦显著不同，沉积物中优势菌门分别为变形菌门、绿弯菌门、酸杆菌门，占总组成50%以上。苦草生长显著增加沉积物群落中变形菌门、脱硫菌门丰度，而降低了酸杆菌门、放线菌门、芽单胞菌门丰度。各环境因子中，溶解氧对沉积物群落组成影响最大，其次是沉积物总磷、有效铁及pH。5）平板培养所得不动杆菌属具有铁氧化功能，而梯度试管所得铁氧化菌群，99%以上主要为未分类的变形杆菌，并具铁氧化、甲烷与甲醇氧化功能。6）等温吸附条件下，细菌氧化铁与针铁矿对溶液磷吸附效率显著高于赤铁矿，以细菌氧化铁吸附效率最高，磷吸附率可达97.6%，且受溶液pH影响较小。