Tracing cyclic redox reactions of Organic Matter in Lakes

这项研究项目将探索淡水生物地球化学的两个组成部分之间以前被忽视的联系：(A)层状湖可以以远洋氧化还原界面为特征。通过这一界面的任何物质都会受到氧气有效性的剧烈变化。(B)微生物在厌氧呼吸中用作终端电子受体(TEA)时，可能会减少溶解有机物(DOM)中的苯醌含量。还原的部分可以在位错到氧环境中被迅速地重新氧化。在以前的工作中，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，氧化的DOM可能会将微生物群落从茶叶限制中释放出来。这一建议建立在一个假设的基础上，即氧化和还原状态之间的快速循环可能是瞬时水域界面上的一种普遍现象。在这些时空生态位中，生物质降解的很大一部分可能与DOM的可逆减少有关。在这里，我们的具体目标是首次量化通过这一途径引导的生态系统呼吸。这项研究将针对温带和北方湖泊，因为它们代表了全球淡水的主要部分，并且通常具有紧密耦合的DOM氧化还原循环所需的物理化学条件。我们预计，由于对包括产甲烷在内的不利呼吸途径的竞争性抑制，温室气体的产生将受到相当大的影响。鉴于陆地有机碳向北部表层水域的输送日益增加，这一机制对预测全球水生二氧化碳和甲烷排放量至关重要。该项目将跨越多个尺度，包括实验室和野外实验，以模拟湖泊环境中DOM与茶叶的相关性。因此，拟议中的加拿大湖泊研究将增加对DOM氧化还原循环的机理的理解，包括它在水生碳周转中的作用。

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.