多环芳烃污染对农田土壤硝化过程的影响及其微生物学机制

Nitrification is one of the central processes of nitrogen cycling. As an important agricultural soil ecosystem service, nitrification is mainly carried out by microorganisms. Polycyclic aromatic hydrocarbons (PAHs) are major persistent organic pollutants in China croplands, which may affect soil nitrification; however, the underlying microbial mechanism remains unclear. In this project, three experiments will be performed to reveal the ecotoxicity of PAHs to nitrifiers. First, nitrification activity and nitrifiers community features will be determined with long-term contaminated agricultural soils collected from areas of intensive PAHs emission. Second, the dose-response relationship between PAHs and nitrifiers will be assessed with acute exposure microcosm study. The third experiment will test the toxicity of PAHs to pure cultures of nitrifiers. In addition, the resistance mechanism of nitrifiers to PAHs will be examined by transcriptomic approach. To evaluate the potential effects of PAHs transformation, long-term microcosm incubation will be established and the toxicity of soil extracts fractions of different polarity will be tested with pure cultured nitrifiers. The aim of this study is to understand the microbial mechanisms underlying the stress of PAHs on soil nitrification, which will facilitate the assessment of ecological risk and the development of biological diagnosis of soil PAHs pollution.

硝化是氮循环的关键环节，主要由微生物驱动，是农田土壤生态系统的重要功能。多环芳烃是我国农田土壤主要污染物之一，对硝化过程具有潜在影响，但微生物学机制尚不清楚。本项目选择我国多环芳烃较高排放地区农田，开展原位调查研究污染土壤中硝化功能及相关微生物的特征，建立土壤微宇宙明确多环芳烃与硝化微生物间的剂量-效应关系，并通过纯培养硝化菌株胁迫实验予以验证，以揭示多环芳烃对硝化微生物的生态毒理效应；通过转录组分析探明常见硝化微生物对多环芳烃的抗性机制；建立长期培养土壤微宇宙，分析不同极性提取物对硝化微生物的毒性变化，对照土壤硝化微生物活性及群落特征，阐明多环芳烃降解转化导致其生态毒性演变的规律。本项目旨在深入了解多环芳烃影响农田土壤硝化的微生物学机制，将有助于全面评价多环芳烃污染的土壤生态效应，为发展土壤污染生物诊断、生态风险评价提供重要科学依据。

硝化是农田土壤氮循环的重要过程，主要由微生物驱动。多环芳烃是我国土壤中常见的有机污染物，但多环芳烃污染对农田土壤的硝化过程具有何种影响、机制如何，目前尚不清楚。本项目开展了下述研究：建立了基于碳同位素示踪污染物转化、氧同位素标记土壤活跃生长微生物以及宏基因组、选择性抑制等较为系统的土壤污染物/微生物研究方法；调查了沈阳、南京、广州三处典型多环芳烃污染土壤中的硝化微生物群落特征及污染物环境归趋；利用土壤微宇宙短期暴露实验，评价了典型四环多环芳烃苯并[a]蒽及其氧化中间产物苯并[a]蒽醌对农田土壤氨氧化微生物群落的影响，并用氨氧化古菌富集菌株进行了验证；设立土壤长期暴露实验，研究了硝化与多环芳烃转化过程间的交互作用；分析了木质素作用下土壤多环芳烃转化的共代谢机制及硝化微生物响应。本项目通过同位素、组学等方法的联合运用，获得了如下重要结果：1、多环芳烃的氧化产物比母体化合物对硝化微生物具有更高的毒性，这可能是多环芳烃产生生态毒性的重要机制；2、土壤硝化和多环芳烃转化过程存在紧密的相互作用，多环芳烃改变土壤中的硝化活性与微生物群落特征，硝化过程也对多环芳烃转化产生重要影响；3、木质素促进多环芳烃的真菌共代谢转化，同时对土壤硝化活性与硝化微生物产生影响。这些结果明确了多环芳烃对硝化微生物的生态毒性及可能作用机制，发现了土壤氮转化和多环芳烃降解之间的复杂相互作用，对于揭示多环芳烃的生态毒性、完整理解土壤环境中氮循环和污染物循环具有重要的科学意义。