State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China.
National-Regional Joint Engineering Research Center for Soil Pollution Control and Remediation in South China, Guangdong Key Laboratory of Integrated Agro-environmental Pollution Control and Management, Institute of Eco-environmental and Soil Sciences, Guangdong Academy of Sciences, Guangzhou 510650, China; School of Environmental Studies, China University of Geosciences, Wuhan 430074, China; State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
Sci Total Environ. 2024 Jun 25;931:172908. doi: 10.1016/j.scitotenv.2024.172908. Epub 2024 May 1.
Shallow lakes, recognized as hotspots for nitrogen cycling, contribute to the emission of the potent greenhouse gas nitrous oxide (NO), but the current emission estimates for this gas have a high degree of uncertainty. However, the role of NO-reducing bacteria (NORB) as NO sinks and their contribution to NO reduction in aquatic ecosystems in response to NO dynamics have not been determined. Here, we investigated the NO dynamics and microbial processes in the nitrogen cycle, which included both NO production and consumption, in five shallow lakes spanning approximately 500 km. The investigated sites exhibited NO oversaturation, with excess dissolved NO concentrations (ΔNO) ranging from 0.55 ± 0.61 to 53.17 ± 15.75 nM. Sediment-bound NO (sNO) was significantly positively correlated with the nitrate concentration in the overlying water (p < 0.05), suggesting that nitrate accumulation contributes to benthic NO generation. High NO consumption activity (R) corresponded to low ΔNO. In addition, a significant negative correlation was found between R and nir/nosZ, showing that bacteria encoding nosZ contributed to NO consumption in the benthic sediments. Redundancy analysis indicated that benthic functional genes effectively reflected the variations in R and ∆NO. qPCR analysis revealed that the clade II nosZ gene was more sensitive to ΔNO than the clade I nosZ gene. Furthermore, four novel genera of potential nondenitrifying NORB were identified based on metagenome-assembled genome analysis. These genera, which are affiliated with clade II, lack genes responsible for NO production. Collectively, benthic NORB, especially for clade II-type NORB, harnesses NO consumption activity leading to low NO emissions from shallow lakes. This study advances our knowledge of the role of benthic clade II-type NORB in regulating NO emissions in shallow lakes.
浅水湖泊被认为是氮循环的热点，它们会向大气中排放一种强温室气体——氧化亚氮（NO），但目前对这种气体的排放估算存在很大的不确定性。然而，反硝化细菌（NORB）作为 NO 的汇及其在水生生态系统中对 NO 动态响应的 NO 还原作用尚未确定。在这里，我们调查了跨越约 500 公里的五个浅水湖泊中的氮循环中包括 NO 产生和消耗在内的 NO 动态和微生物过程。所研究的地点都表现出 NO 过饱和，过量溶解的 NO 浓度（ΔNO）范围从 0.55 ± 0.61 到 53.17 ± 15.75 nM。沉积物结合态 NO（sNO）与上覆水中的硝酸盐浓度呈显著正相关（p < 0.05），这表明硝酸盐的积累有助于底栖 NO 的产生。高的 NO 消耗活性（R）对应于低的ΔNO。此外，R 与 nir/nosZ 之间还发现了显著的负相关，这表明编码 nosZ 的细菌有助于底栖沉积物中的 NO 消耗。冗余分析表明，底栖功能基因能有效反映 R 和 ∆NO 的变化。qPCR 分析表明，clade II nosZ 基因比 clade I nosZ 基因对 ΔNO 更敏感。此外，基于宏基因组组装基因组分析，还鉴定了四个潜在的非反硝化 NORB 的新属。这些属与 clade II 有关，缺乏负责 NO 产生的基因。总之，底栖 NORB，特别是 clade II 型 NORB，利用 NO 消耗活性，导致浅水湖泊中 NO 的排放量较低。本研究提高了我们对底栖 clade II 型 NORB 在调节浅水湖泊中 NO 排放中的作用的认识。
