Collaborative Research: Coupled Geochemical and Geobiological Characterization of Dissolved Organic Matter Oxidation to Carbon Dioxide

溶解在水生生态系统中的有机分子代表了通过河流网络运输的最大有机物质库，也是地球上最复杂的混合物之一。微生物对这些有机分子的处理导致它们转化为二氧化碳，这有助于在水生环境和大气之间进行大量的二氧化碳交换，对全球气候变化具有影响。尽管这一现象很重要，但多达80%易受微生物代谢影响的有机碳仍未被识别。本研究的目标是利用低通量、超高分辨率分析有机化学的最新进展来识别和表征生物活性分子池，并扩展常用的高通量、低分辨率光学技术的能力，以提供有关这些分子在河流网络中的时间动态的信息。这项研究的结果可以促进对河网中有机分子组成与二氧化碳向大气逃逸之间联系的理解，回答是什么使有机分子可生物降解的问题。研究人员将与教授K-12学生的教育工作者合作，使肉眼看不见的过程变得容易理解和引人注目，因为教育工作者开发的课程描绘了分子地球化学和微生物地球生物学对地球上生命的影响。研究人员假设：(1)细菌呼吸到二氧化碳的溶解有机物大部分是具有生物活性但分子特征不明显的腐殖质分子；(2)通过使用先进的统计分析，包括斯皮尔曼秩和二维相关分析，可以将有色或荧光溶解有机物的成分与单个分子式组相关联；(3)在遥远的流域中普遍存在的溶解有机物分子跨越了生物反应谱，而流域特有的分子主要是反应性的，很容易转化为二氧化碳。该研究将在两个特征鲜明的河流流域内的溪流中进行，一个在宾夕法尼亚州的温带森林中，一个在哥斯达黎加的热带常绿森林中。水样将在基流和暴雨流条件下收集，跨越溪流顺序和季节，并使用溪流供水的塞流生物反应器将其分为生物反应性类别。样品将使用傅里叶变换离子回旋共振质谱以及紫外可见吸光度和荧光光谱与激发发射矩阵进行分子表征。这项研究的成功完成将提高使用光学传感器来了解河流网络中的碳流的能力，并提高对溶解有机物质的分子性质的理解，这些物质促使二氧化碳从溪流和河流逃逸到大气中。

Organic molecules dissolved in aquatic ecosystems represent the largest pool of organic matter transported through river networks and one of the most complex mixtures on Earth. The processing of these organic molecules by microorganisms resulting in their conversion to CO2 contributes to the large exchange of CO2 between the aquatic environment and the atmosphere with implications for global climate change. Despite the importance of this phenomenon, as much as 80% of the organic carbon susceptible to microbial metabolism remains unidentified. The goals of this study are to use recent advances in low through-put, ultra-high resolution analytical organic chemistry to identify and characterize the pool of biologically reactive molecules and to extend the ability of commonly used high through-put, low-resolution optical techniques to provide information about the temporal dynamics of these molecules in river networks. The outcomes of this research could advance the understanding of the link between the composition of organic molecules in a river network and the evasion of CO2 to the atmosphere, answering the question of what makes an organic molecule biodegradable. The researchers will work with educators who teach K-12 students in making processes that are invisible to the naked eye accessible and compelling as the educators develop curricula that depict the influence of molecular geochemistry and microbial geobiology to life on Earth.The researchers hypothesize that: (1) biologically reactive but molecularly uncharacterized humic molecules account for the majority of dissolved organic matter that bacteria respire to CO2; (2) the constituents of colored or fluorescent dissolved organic matter can be associated with groups of individual molecular formulas through the use of advanced statistical analyses, including Spearman Rank and 2-D correlation analyses; and (3) dissolved organic matter molecules that are ubiquitous across distant watersheds span the biological reactivity spectrum, while molecules unique to a watershed are predominantly reactive and readily converted to CO2. The research will be performed in streams within 2 well characterized river basins, one in the temperate forests of Pennsylvania and one in the tropical evergreen forests of Costa Rica. Water samples will be collected under baseflow and storm flow conditions, across stream orders and seasons, and separated into biological reactivity classes using stream water-fed plug flow bioreactors. The samples will be molecularly characterized using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry as well as UV-visible absorbance and fluorescence spectra with excitation emission matrices. The successful completion of the research should advance the ability to use optical sensors to understand carbon flow through river networks and advance the understanding of the molecular nature of the dissolved organic matter that fuels the evasion of CO2 from streams and rivers to the atmosphere.