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

内陆沃茨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接收的大量有机物质。溶解的有机物影响这些沃茨的颜色和健康，并为水生食物网提供外部能量。OM的命运在很大程度上取决于其在这些沃茨中的反应性：由于氧化和矿化为CO2是最终的OM汇过程，传统的范式认为氧气的可用性作为OM反应性和营业额的关键控制。然而，在缺氧（缺氧）沃茨中，有机物的生产、加工和转化也非常活跃。OM的化学结构和组成被转化的一系列途径是缺氧所独有的，包括（1.）富含能量的有机物组分优先降解，（2.）破坏微生物OM的再循环，和（3.）与来自厌氧菌的氢气（H2）反应。目前，尚不清楚这些途径在何种条件下发生，多种途径是否相互作用，以及它们如何影响内陆沃茨碳的最终命运。这种缺乏了解的情况仍然存在，尽管缺氧条件在淡水走廊广泛存在，全球变暖和富营养化预计将进一步增加缺氧的持续时间和范围。因此，该项目的中心目标是对缺氧环境中转化DOM的生态和生物地球化学驱动因素进行分类。为此，我们开发了一个新的框架的基础上，机械有意义的，化合物水平的自由能（ΔG）特性的OM使用大型化合物数据库。我们首先使用这种基于能量的框架来概念化孤立的不同缺氧转化途径，然后在复杂的环境样品中追踪多种途径。这为找到特定于地区和基质的因素（例如，能量的可用性，缺氧的时间尺度），随着缺氧中观察到的OM组成变化而变化。最后，将分析大型环境数据集，以评估缺氧在土壤-海洋连续体过程中在OM中留下的潜在水平印记。该项目的成果将为水生系统中OM循环的新能源中心观点铺平道路，从而更准确地分析其生物和非生物处理，并将OM转化途径与生态系统和研究社区联系起来。

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.