E=OC^2 – Energy resolves Organic Carbon Complexity in anoxic waters

内陆水域是全球碳循环的重要组成部分，因为它们运输和处理从陆地生物圈获得的大量有机物质。溶解的OM影响这些水域的颜色和健康，并为水生食物网提供外部能量。有机质的命运在很大程度上取决于其在这些水域中的反应性：因为氧化和矿化为二氧化碳是最终的有机质下沉过程，传统的范式认为氧气的可用性是对有机质的反应性和周转的关键控制。然而，在缺氧(缺氧)水域中也有非常活跃的OM的生产、加工和转化。有机质的化学结构和组成的一系列转化途径是缺氧所特有的，包括(1)高能OM组分的优先降解，(2)破坏了微生物OM的循环，以及(3)与厌氧菌产生的氢(H2)反应。目前，尚不清楚这些途径是在什么条件下发生的，是否有多条途径相互作用，以及它们如何影响内陆水域碳的最终命运。尽管淡水走廊普遍存在缺氧情况，而且全球变暖和富营养化预计将进一步增加缺氧持续时间和范围，但这种缺乏了解的情况仍然存在。因此，该项目的中心目标是对在缺氧环境中转化DOM的生态和生物地球化学驱动因素进行分类。为此，我们使用大型化合物数据库开发了一个新的框架，该框架基于OM的具有力学意义的化合物能级自由能(ΔG)特性。我们首先使用这个基于能量的框架来孤立地概念化不同的缺氧转化途径，然后在复杂的环境样本中追踪多条途径。这为找到特定于现场和底物的因素(例如，能量的可获得性、缺氧的时间尺度)奠定了基础，这些因素随着在缺氧中观察到的OM成分变化而变化。最后，将分析大型环境数据集，以评估缺氧在OM中通过土壤-海洋连续体期间留下的景观级印记。该项目的成果将为在水生系统中以能源为中心的有机质循环的新视角铺平道路，从而能够更准确地分析其生物和非生物过程，并将跨生态系统和研究社区的有机质转化途径联系起来。

Inland waters are an important component of the global carbon cycle because they transport and process large amounts of organic matter (OM) which they receive from the terrestrial biosphere. Dissolved OM affects the color and health of these waters, and supplies the aquatic food web with external energy. The fate of OM largely depends on its reactivity in these waters: Because oxidation and mineralization to CO2 is the ultimate OM sink process, the conventional paradigm considers oxygen availability as a critical control on OM reactivity and turnover. However, there is very active production, processing and transformation of OM also in anoxic (oxygen-deprived) waters. A range of pathways on which the chemical structure and composition of OM is transformed are exclusive to anoxia, including (1.) the preferential degradation of energy-rich OM fractions, (2.) disrupted recycling of microbial OM, and (3.) reaction with hydrogen (H2) from anaerobes. Currently, it is unclear under which conditions these pathways occur, if multiple pathways interact and how they affect the ultimate fate of carbon in inland waters. This lack of understanding persists, despite anoxic conditions are widespread in the freshwater corridor, and global warming and eutrophication have been predicted to further increase anoxia duration and range. The central aim of this project is thus to classify the ecological and biogeochemical drivers that transform DOM in anoxic environments. To this end, we develop a novel framework based on mechanistically meaningful, compound-level free energy (ΔG) characteristics of OM using large compound databases. We use this energy-based framework first to conceptualize distinct anoxic transformation pathways in isolation, and later to trace multiple pathways in complex environmental samples. This builds the foundation to find the locale- and substrate-specific factors (e.g., availability of energy, timescales of anoxia) that vary with OM compositional changes observed in anoxia. Finally, large environmental datasets will be analyzed to assess the landscape-level imprint that anoxia leaves in OM during its passage of the soil-to-ocean continuum. The outcome of this project will pave the way for a novel energy-centric perspective of OM cycling in aquatic systems, allowing for a more accurate analysis of its biotic and abiotic processing and to link OM transformation pathways across ecosystems and research communities.