Hubei Key Laboratory of Industrial Biotechnology, College of Life Sciences, Hubei University, 430062 Wuhan, China.
School of Energy & Environmental Engineering, University of Science and Technology Beijing, 100083 Beijing, China.
Sci Total Environ. 2018 Dec 10;644:747-753. doi: 10.1016/j.scitotenv.2018.06.382. Epub 2018 Jul 11.
The ocean is an important source of methane, however, the sources of oceanic methane and mechanisms of its release to the atmosphere have only recently begun to be understood. Recent studies have identified methylphosphonate (MPn) as a previously unknown and likely source of methane in the aerobic ocean (Karl et al., 2008), as well as shown the biosynthesis of methylphosphonic acid to be a widespread trait in marine microbes (Metcalf et al., 2012). The mechanisms and reaction pathways from MPn to free methane, however, have not been well studied. Here we present results of laboratory studies on the photo-degradation of MPn, a likely mechanism of methane release to the atmosphere and phosphate release to the surface oceans. Phosphonoacetic acid was also studied as an additional model compound for comparison. We used the multi-labeled water isotope probing (MLWIP) approach, involving O-labeled waters to probe the photolytic mechanism of CP bond cleavage in phosphates through analysis of P released from MPn as PO. These studies identified distinct reaction pathways involving phosphates compared with other common organophosphorus compounds (e.g., phosphoesters), as well as suggest the involvement of both ambient water and atmospheric oxygen in CP bond cleavage. There is only a small amount of water oxygen incorporated into product PO after cleavage of the CP bond in MPn, suggesting atmospheric O or radicals formed from O under Ultra Violet Radiation (UVR), as the primary source of O that replaces C in the CP bond of MPn. Model calculations suggest that the δO signature of phosphate released via UV-degradation of phosphates is largely (75%) inherited from the original phosphate substrate. This opens up the possibility of tracing and differentiating specific phosphate sources of dissolved phosphate from other organophosphorus (Porg) sources (e.g., phosphoesters) used in primary production, as well as for tracing specific MPn sources of atmospheric methane.
海洋是甲烷的一个重要来源，然而，海洋甲烷的来源及其向大气释放的机制直到最近才开始被人们所了解。最近的研究已经确定甲基膦酸酯（MPn）是有氧海洋中甲烷的一个以前未知的可能来源（Karl 等人，2008 年），并表明甲基膦酸的生物合成是海洋微生物中广泛存在的特征（Metcalf 等人，2012 年）。然而，从 MPn 到游离甲烷的机制和反应途径尚未得到很好的研究。在这里，我们介绍了实验室对 MPn 光降解的研究结果，MPn 是甲烷向大气释放和磷酸盐向表层海洋释放的一种可能机制。我们还研究了膦酸作为附加模型化合物进行比较。我们使用多标记水同位素探测（MLWIP）方法，涉及 O 标记水，通过分析从 MPn 中释放的 PO 来探测磷酸盐中 CP 键断裂的光解机制。这些研究确定了与其他常见有机磷化合物（例如，磷酸酯）相比，涉及磷酸盐的独特反应途径，并且表明 CP 键断裂中大气氧和环境水的参与。在 MPn 的 CP 键断裂后，只有少量的水氧掺入到产物 PO 中，这表明大气氧或紫外线辐射（UVR）下形成的自由基是取代 MPn 中 CP 键中 C 的主要来源。模型计算表明，通过磷酸盐的紫外线降解释放的磷酸盐的 δO 特征主要（75%）继承自原始磷酸盐底物。这为追踪和区分溶解磷酸盐中特定磷酸盐来源与其他用于初级生产的有机磷（Porg）来源（例如，磷酸酯）开辟了可能性，以及追踪大气甲烷中特定的 MPn 来源。
