富营养化湖泊挺水植物对根际沉积物氨氧化过程影响的微生物学机理

Emergent macrophytes are crucial components of lake ecosystems and play important roles in the nitrogen cycling process. Previous studies have mainly focused on the chemical process of the transportation and transformation of nitrogen induced by the emergent macrophytes. However, little is known about the microbial mechanisms involved in these processes. In this proposed study, the commonly found emergent macrophytes (Phragmites communis and Zizamia caduciflora) in Lake Taihu were chosen to examine the effects of emergent macrophytes on ammonia oxidation (the rate limiting step of nitrification) in their rhizosphere sediments. Molecular biology, microelectrodes, 15N isotope tracer and the quantitative ecology methods would be employed to study the ecological distributions of microorganisms involved in the ammonia oxidation process and their responses to the variable environmental factors. Field study will be performed firstly to investigate the seasonal variations of the ammonia-oxidizing prokaryotes in the rhizosphere sediments of emergent macrophytes in Lake Taihu. Microcosm experiments will subsequently be carried out to compare the effects of different emergent macrophyte species and environmental factors (nutrients, pH and organic matters) on the abundance, community composition and activity of the ammonia-oxidizing prokaryotes, which may be attributed to the differences of nitrogen adsorption, release of oxygen and other exudates via the roots during the growth of emergent macrophytes. The obtained results would be helpful to elucidate the microbial mechnisms of emergent macrophytes affecting the ammonia oxidation process in lake sediments. The results are also useful to better understand the functions of emergent macrophytes in lake ecosystems and would provide basic theory for the bioremediation of eutrophic lakes.

挺水植物是湖泊生态系统的重要组成部分，对湖泊氮循环过程有重要影响。国内外现有研究主要关注挺水植物对氮素迁移转化影响的化学过程，很少涉及其中的微生物学机理。本课题以富营养化湖泊太湖中常见的挺水植物芦苇和菰为研究对象，以硝化作用的限速步骤好氧氨氧化过程为研究内容，结合分子生物学、微电极检测、氮同位素示踪及数量生态学等多种技术手段和方法，首先进行野外调查，研究不同季节太湖挺水植物根际沉积物中氨氧化原核生物的生态分布及其对环境因子的响应规律。然后通过模拟实验，从挺水植物生长过程中根系吸收氮素、释放氧及其它分泌物等方面，深入探讨不同种类挺水植物以及不同环境条件（营养盐水平、pH及有机质含量）对根际沉积物中氨氧化原核生物丰度、群落结构及活性影响的差异性。预期成果将阐明挺水植物对沉积物中好氧氨氧化过程影响的微生物学机理，有助于深化对挺水植物在湖泊生态系统中功能的认识，为富营养化水体治理提供基础理论参考。

挺水植物和微生物都是湖泊生态系统的重要组成部分，对湖泊中氮、磷等生源要素的生物地球化学循环过程都有着重要影响。本课题以富营养化湖泊太湖中常见的挺水植物芦苇和茭草为研究对象，以硝化作用的限速步骤好氧氨氧化过程为研究内容，应用高通量测序、实时荧光定量PCR、构建克隆文库以及数量生态学分析等多种技术手段和分析方法，研究了挺水植物对其根际沉积物中总细菌及氨氧化原核生物丰度、群落组成的影响。结果表明：（1）茭草（Zizania caduciflora）和芦苇（Phragmites australis）的根际沉积物细菌群落的α多样性与群落组成都显著区别于非根际沉积物中的细菌群落（P < 0.05），与表层沉积物中的细菌群落较为相似（P > 0.05）。环境因子与α多样性指数之间存在较好的线性正相关关系（P < 0.05）。pH、总氮、总磷与氨氮是影响根际环境中细菌群落组成的主要环境因子。（2）挺水植物根际沉积物中的细菌amoA基因的丰度高于空白对照沉积物。潜在硝化率（PNR）与细菌amoA基因的丰度呈显著正相关，表明氨氧化细菌（AOB）可能在挺水植物根际沉积物的硝化过程中起重要作用。Nitrosotalea是氨氧化古菌（AOA）中的优势类群；AOB的群落组成分析表明：N. europaeal是茭草根际沉积物和空白对照沉积物中的优势类群，而Nitrosospira是芦苇根际沉积物中的优势类群。（3）此后，探究了冬季（1月）和夏季（8月）两种挺水植物根际沉积物中AOA和AOB的丰度和群落组成。在大部分样品中，古菌amoA基因的丰度均高于细菌amoA基因丰度。冬季芦苇根际沉积物中古菌和细菌amoA基因丰度均为最高。相关分析结果表明：细菌amoA基因丰度显著正相关于NO3--N（P < 0.05）。