太湖固氮蓝藻时空特征的生理生态学机制研究

Cyanobacterial blooms have become the major environmental problem in the freshwater lakes. Bloom-forming cyanobacteria include nitrogen-fixing and non-nitrogen-fixing species. Nitrogen-fixing cyanobacteria are critical contributor to the nitrogen pool in oceanic waters and their contribution in lake ecosystems, especially eutrophic lakes are still controversial. The mechanisms for spatiotemporal changes and ecophysiological characteristics of nitrogen-fixing cyanobacteria in lake waters were still not revealed， and whether the nitrogen-fixing cyanobacteria could fix nitrogen . The present project will focus on Taihu Lake, the typical eutrophic lake in China, to study the spatiotemporal characteristics of nitrogen-fixing cyanobacteria and their relationship with the environmental factors (such as water temperature, pH, TN, NH3-N, NO3-N, TP and PO4-P). The clone libraries of nitrogenase gene expression in situ will be constructed. Dominant nitrogen-fixing cyanobacteria will be quantified and their nitrogen-fixation rates will be detected in typical lake regions. Then the effects of nitrogen-fixing cyanobacteria on nitrogen pool of lake waters will be evaluated. Meanwhile, nitrogen-fixing strains with dominant genotype will be isolated using the Micropipet method followed by continuous washing. The nitrogen-fixing ability of dominant strains/genotypes under different environmental conditions (temperature, day-night period and nutrient salts) will be characterized to explore inner-driving mechanism of competitive advantage for dominant strains. Finally, the important experimental and theoretical basis could be provided on the effects of nitrogen-fixing cyanobacteria on nitrogen pool of fresh waters.

蓝藻水华是淡水湖泊的一大环境问题，构成蓝藻水华的种类可以分为固氮与非固氮两大类群。固氮蓝藻是海洋氮库重要的贡献者，而对于湖泊生态系统尤其是富营养状态下的湖泊，固氮蓝藻的贡献还存在较大争议，具有固氮能力的蓝藻是否行使固氮特性，固氮蓝藻的时空变化规律及其生理生态机制还未被揭示。本研究以典型富营养化湖泊——太湖为例，在前期研究基础上，通过对典型固氮蓝藻的定量分析，并结合构建固氮酶基因表达的克隆文库、定量优势固氮蓝藻基因拷贝数和固氮率测定，对典型湖区的固氮蓝藻及其固氮特性进行检测，分析其时空变化特征，探讨其与环境因子（温度、pH、总氮、氨氮、硝态氮、总磷及正磷酸盐）的相关关系；同时，利用单藻株分离技术筛选出优势基因型匹配的固氮藻株，研究其在不同温度、昼夜变化和营养盐比例条件下的固氮特性，探讨影响行使固氮特性的藻株的关键因子及内在机制，为揭示固氮蓝藻对淡水水体氮库的影响提供重要的实验和理论依据。

蓝藻水华是淡水湖泊的一大环境问题，构成蓝藻水华的种类可以分为固氮与非固氮两大类群。固氮蓝藻是海洋氮库重要的贡献者，而对于湖泊生态系统尤其是富营养状态下的湖泊，固氮蓝藻的贡献还存在较大争议，具有固氮能力的蓝藻是否行使固氮特性，固氮蓝藻的时空变化规律及其生理生态机制还未被揭示。基于此，本项目针对太湖固氮蓝藻的时空特征的生理生态学进行研究，旨在揭示太湖固氮蓝藻及其对太湖氮库影响。研究结果表明太湖固氮蓝藻具有时空分布特征，冬春分布较高，峰值达到5.0×107个/升，并对其不同的ITS基因型研究发现，太湖固氮蓝藻呈现两型交替现象；同时，对太湖水体进行了原位固氮率的检测，并成功分离固氮藻株，对其进行了固氮检测，发现其固氮活性极低，同时对其进行室内生理检测和驯化实验，推测太湖水华长胞藻可能在野外失去了固氮能力，水华长胞藻对太湖氮库贡献极低。