Tracing cyclic redox reactions of Organic Matter in Lakes

本研究项目将探讨以前被忽视的淡水地球化学两个组成部分之间的联系：（a）分层湖泊可以具有远洋氧化还原界面。任何通过这个界面的物质都会受到氧气可用性的剧烈变化。(b)微生物在厌氧呼吸中作为末端电子受体（TEA）时，可还原溶解有机物（DOM）中的醌部分。在早期的研究中，DOM的微生物还原和随后的非生物氧化被证明是可逆的。此外，氧化DOM可以释放微生物群落从TEA限制。这一建议建立在这样的假设之上，即氧化和还原状态之间的快速循环可能是瞬态水生界面的一种普遍现象。在这些时空生态位中，生物量退化的一个显着的份额可能是耦合到DOM的可逆减少。在这里，我们专门针对通过这一途径的生态系统呼吸的第一个量化。该研究将解决温带和北方湖泊，因为它们代表了全球淡水沃茨的主要部分，通常具有紧密耦合DOM氧化还原循环所需的物理化学条件。我们预计相当大的影响，温室气体的生产，由于竞争性抑制不利的呼吸途径，包括甲烷。鉴于陆地有机碳向北方表层沃茨的输送日益增加，这一机制对于预测全球水生二氧化碳和甲烷排放至关重要。该项目将跨越多个尺度，包括实验室和现场实验，以模拟湖泊环境中呼吸与DOM作为TEA的相关性。因此，拟议中的研究在加拿大湖泊将增加DOM氧化还原循环的机械理解，包括其在水生碳周转的作用。

This research project will explore a previously disregarded linkage between two components of freshwater biogeochemistry:(a) Stratified lakes can feature pelagic redox interfaces. Any matter that passes through this interface is subjected to drastic changes in oxygen availability.(b) Microorganisms may reduce quinone moieties in dissolved organic matter (DOM) when used as terminal electron acceptor (TEA) in anaerobic respiration. The reduced moieties may be rapidly re-oxidized upon dislocation to oxic environments.In earlier works, the microbial reduction and subsequent abiotic oxidation of DOM was shown to occur reversibly. Also, the oxidized DOM may release microbial communities from TEA limitation. This proposal builds on the hypothesis that the rapid cycling between oxidized and reduced states may be a widespread phenomenon at transient aquatic interfaces. In these spatiotemporal niches, a significant share of biomass degradation might be coupled to the reversible reduction of DOM. Here, we specifically aim for the first quantification of ecosystem respiration channeled through this pathway. The research will address temperate and boreal lakes since they represent a major fraction of global fresh waters and typically feature the physicochemical conditions necessary for tightly coupled DOM redox cycles. We expect considerable implications for greenhouse gas production due to the competitive inhibition of less favorable respiration pathways including methanogenesis. In light of the increasing transport of terrestrial organic carbon to boreal surface waters, this mechanism is critical to the prediction of global aquatic carbon dioxide and methane emissions.The project will span multiple scales and include laboratory and field experiments to model the relevance of respiration with DOM as TEA in lacustrine environments. Hence, the proposed research across Canadian lakes will increase the mechanistic understanding of DOM redox cycling including its role in aquatic carbon turnover.