单一及复合PAHs污染对铜绿微囊藻氮素吸收的影响及生物机制

Nitrogen is demonstrated to be the essential nutrient for phytoplankton growth, which is also defined as the key factor to induce eutrophication of lakes. The potential ecological effects of polycyclic aromatic hydrocarbons (PAHs) on phytoplankton physiology and their related nutrient biogeochemical processes have attracted much more attention from scientists. However, no information on how such pollutants will influence the nitrogen uptake by phytoplankton can be found anywhere. In the present project, the single and combined pollution of two typical PAHs (Naphthalene and Phenantherene, Nap and Phe) on Microsystis aeruginosa will be investigated by the laboratory microcosm study and field mesocosm experiments. Several physiological biomarkers such as growth rates, photosynthesis rates, cell viability and antioxidant enzyme activities are tested to elucidate the toxic effects of PAHs on Microcystis aeruginosa. In addition, stable nitrogen isotope labeling coupled with isotope mass spectrometer are used to imply the response of nitrogen uptake rate and internal kinetic processes to PAH pollution. And then, the internal mechanisms focused on biological aspects are discussed by analyzing the key enzyme activities (H+-ATP enzyme, glutamine synthetase, nitrate reductase, urease and L-amino acid oxidase) related to nitrogen uptake and assimilation by phytoplankton. Through the whole project, the potential toxic effects of PAHs on both the physiological characteristics of phytoplankton and the following physiochemical processes involved can be demonstrated, which is necessary for eutrophication mechanism exploring and ecological risk assessment of PAHs in lake ecosystems.

氮是浮游藻类的重要生源物质，也是导致湖泊富营养化的关键要素之一。多环芳烃(PAHs)是水体广泛赋存的微量有毒化合物，对浮游藻类生理过程的影响及其生物毒性已有一定研究基础，但是，PAHs污染对浮游藻类氮素吸收的影响效应和作用机制未知，阻碍了对水体氮素循环，特别是氮素吸收过程及机制的完整认识。本项目以PAHs污染生态环境效应为出发点，选取铜绿微囊藻为研究对象，结合室内染毒培养和野外原位实验，从藻类生长率、光合作用率、细胞活性及抗氧化酶活性等生理指标入手，阐明PAHs污染对铜绿微囊藻的生理毒性；进一步运用稳定氮同位素标记技术，弄清PAHs对藻类氮素吸收率和动力学过程的影响效应；结合藻类氮素吸收同化过程关键酶活分析，探讨藻类氮素吸收对PAHs污染的生物学响应机制，揭示单一及复合PAHs污染对铜绿微囊藻生理特性及其生化过程的影响，完善湖泊富营养化发生机制，并为开展PAHs生态风险评价提供科学依据。

多环芳烃PAHs污染对湖泊生态系统初级生产者浮游植物生长生理及其参与生态功能过程的影响是全面评价湖泊PAHs污染生态效应和健康风险的重要方面。本研究采用稳定氮同位素示踪技术（15N），通过室内染毒培养和野外原位实验，明确了铜绿微囊藻生长生理特性对单一及复合PAHs污染的响应特征，细胞抗氧化酶系统损伤或应激反应是微囊藻应对污染胁迫的主要内在机制，且存在一定的时间-效应和浓度-效应关系；研究了单一及复合PAHs污染胁迫下铜绿微囊藻对不同形态氮素（NO3-N、NH4-N及尿素Urea-N）吸收速率的响应过程，其中，NO3-N吸收对Phe污染胁迫响应敏感，呈现毒物的兴奋效应，还原态氮形态NH4-N和Urea则表现出对Pyr及Phe&Pyr复合污染的响应更为显著；结合氮素吸收代谢关键酶活指标（H+-ATPase、NR和GS）分析，揭示了PAHs污染物通过影响藻细胞生长作用、光合作用、呼吸作用、电子传递及能量过程等，引起藻细胞氮吸收转运-吸收-代谢酶活改变，进而影响氮素吸收速率，构建了PAHs污染对藻细胞氮素吸收代谢的影响概念模型；考察了太湖典型湖区水体氮素吸收速率时空变化规律，入湖口及梅梁湾等富营养化湖区氮素吸收速率较高，NH4-N和Urea吸收与低环PAHs化合物含量相关，NO3-N吸收则主要受高环化合物影响，初步揭示了水体氮素吸收响应对浮游植物种群优势种及群落结构的潜在效应。