Chen Xin, Zhang Sibo, Liu Jiao, Wang Junfeng, Xin Yuan, Sun Siyue, Xia Xinghui
Key Laboratory of Water and Sediment Sciences of Ministry of Education, State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China.
Guangdong Provincial Key Laboratory of Water Quality Improvement and Ecological Restoration for Watersheds, Institute of Environmental and Ecological Engineering, Guangdong University of Technology, Guangzhou, Guangdong 510006, China.
Environ Sci Technol. 2023 May 9;57(18):7196-7205. doi: 10.1021/acs.est.3c00950. Epub 2023 Apr 25.
Nitrous oxide (NO), a potent greenhouse gas, is produced in rivers through a series of microbial metabolic pathways. However, the microbial source of NO production and the degree of NO reduction in river systems are not well understood and quantified. This work investigated isotopic compositions (δN-NO and δO-NO) and NO site preference as well as NO-related microbial features, thereby differentiating the importance of nitrification, denitrification, and NO reduction in controlling NO emissions from five rivers on the eastern Qinghai-Tibet Plateau (EQTP). The average NO concentration in overlying water (15.2 nmol L) was close to that in porewater (17.5 nmol L), suggesting that both overlying water and sediment are potentially important sources of NO. Canonical and nitrifier denitrification dominated riverine NO production, with contribution being approximately 90%. Nitrification is a non-negligible source of NO production, and NO concentration was positively correlated with nitrification genetic potential. The degree of NO reduction ranged from 78.1 to 94.1% (averaging 90%), significantly exceeding the reported values (averaging 70%) in other freshwaters, which was attributed to the higher ratios of organic carbon to nitrogen and lower ratio of ( + )/ in EQTP rivers. This study indicates that a combination of isotopic and isotopocule values with functional microbe analysis is useful for quantifying the microbial sources of NO in rivers, and the intense microbial reduction of NO significantly accounts for the low NO emissions observed in EQTP rivers, suggesting that both the production and consumption of NO in rivers should be considered in the future.
一氧化二氮（N₂O）是一种强效温室气体，通过一系列微生物代谢途径在河流中产生。然而，河流系统中N₂O产生的微生物来源以及N₂O还原程度尚未得到充分理解和量化。这项工作研究了同位素组成（δ¹⁵N-N₂O和δ¹⁸O-N₂O）、N₂O位点偏好以及与N₂O相关的微生物特征，从而区分了硝化作用、反硝化作用和N₂O还原在控制青藏高原东部（EQTP）五条河流N₂O排放中的重要性。上覆水中的平均N₂O浓度（15.2 nmol/L）与孔隙水中的浓度（17.5 nmol/L）相近，这表明上覆水和沉积物都是N₂O潜在的重要来源。典型反硝化作用和硝化细菌反硝化作用主导了河流N₂O的产生，贡献约为90%。硝化作用是N₂O产生的一个不可忽视的来源，N₂O浓度与硝化遗传潜力呈正相关。N₂O还原程度在78.1%至94.1%之间（平均为90%），显著超过其他淡水报道的值（平均为70%），这归因于EQTP河流中较高的有机碳氮比和较低的（+）/（-）比值。这项研究表明，将同位素和同位素分子值与功能微生物分析相结合，有助于量化河流中N₂O的微生物来源，并且强烈的微生物N₂O还原显著解释了EQTP河流中观察到的低N₂O排放，这表明未来应同时考虑河流中N₂O的产生和消耗。
