近日，美国加州大学圣克鲁斯分校 Broek, Taylor A. B. 及其研究团队揭示了循环和持久性的新范例，即海洋中溶解有机氮的主要杂环成分。相关论文发表在2023年11月28日出版的《美国科学院院刊》杂志上。

研究团队首次报道了贯穿两个大洋盆地的水柱分离的低分子量、溶解有机氮的同位素和固体核磁共振结构耦合分析。总之，这些结果提供了对海洋溶解有机氮主要部分的组成、潜在来源和循环的初步看法。研究数据显示，难溶性的海洋溶解有机氮主要以 ¹⁵N-贫杂环-N 结构为主，与先前表征的高分子量的材料完全不同。

这种关于海洋溶解有机氮组成的全新观点表明，在海洋中的积累和持续的难溶性的海洋溶解有机氮，存在一个重要的结构控制。这些含氮杂环化合物的产生、循环和去除机制是当前研究组理解海洋溶解有机氮储层的主要挑战。

据了解，海洋溶解有机氮(DON)是地球上最大的固定氮储存库之一，即使在氮有限的海洋贫营养表层中也能持续存在。总海洋溶解有机氮储层的绝大部分是难溶性的海洋溶解有机氮(RDON)，主要由地下和深海中的低分子量(LMW)化合物组成。然而，这一主要氮库的组成及其积累和持续的原因尚不清楚。过去的表征分析更易于处理，但定量较小，高分子量(HMW) 海洋溶解有机氮级分的表征，揭示了其具有功能上简单的酰胺主导的成分。虽然在过去二十年里，大量的工作揭示了低分子量溶解有机碳的巨大复杂性和结构多样性，但没有进行专门针对低分子量氮分子的工作。

附：英文原文

Title: Dominant heterocyclic composition of dissolved organic nitrogen in the ocean: A new paradigm for cycling and persistence

Author: Broek, Taylor A. B., McCarthy, Matthew D., Ianiri, Hope L., Vaughn, John S., Mason, Harris E., Knapp, Angela N.

Issue&Volume: 2023-11-28

Abstract: Marine dissolved organic nitrogen (DON) is one of the planet’s largest reservoirs of fixed N, which persists even in the N-limited oligotrophic surface ocean. The vast majority of the ocean’s total DON reservoir is refractory (RDON), primarily composed of low molecular weight (LMW) compounds in the subsurface and deep sea. However, the composition of this major N pool, as well as the reasons for its accumulation and persistence, are not understood. Past characterization of the analytically more tractable, but quantitatively minor, high molecular weight (HMW) DON fraction revealed a functionally simple amide-dominated composition. While extensive work in the past two decades has revealed enormous complexity and structural diversity in LMW dissolved organic carbon, no efforts have specifically targeted LMW nitrogenous molecules. Here, we report the first coupled isotopic and solid-state NMR structural analysis of LMW DON isolated throughout the water column in two ocean basins. Together these results provide a first view into the composition, potential sources, and cycling of this dominant portion of marine DON. Our data indicate that RDON is dominated by ¹⁵N-depleted heterocyclic-N structures, entirely distinct from previously characterized HMW material. This fundamentally new view of marine DON composition suggests an important structural control for RDON accumulation and persistence in the ocean. The mechanisms of production, cycling, and removal of these heterocyclic-N-containing compounds now represents a central challenge in our understanding of the ocean’s DON reservoir.

DOI: 10.1073/pnas.2305763120

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2305763120