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是通过河流网络运输的最大有机物质池，也是地球上最复杂的混合物之一。微生物对这些有机分子进行处理，使其转化为二氧化碳，有助于水环境和大气之间二氧化碳的大量交换，并对全球气候变化产生影响。尽管这一现象很重要，但多达80%的易受微生物代谢影响的有机碳仍未确定。这项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，以提供关于河网中这些分子的时间动力学的信息。这项研究的结果可能会促进对河流网络中有机分子组成与二氧化碳向大气的逃逸之间联系的理解，回答了是什么使有机分子可生物降解的问题。研究人员将与教育工作者合作，在教育工作者开发描述分子地球化学和微生物地球生物学对地球上生命的影响的课程时，教会K-12学生使肉眼不可见的过程变得容易和令人信服。研究人员假设：(1)具有生物活性但没有分子特征的腐殖质分子占细菌呼吸二氧化碳的大部分溶解有机物；(2)有色或荧光溶解有机物的成分可以通过使用先进的统计分析，包括Spearman Rank和2-D相关分析，与一组单独的分子式相关联；以及(3)在遥远的分水岭上普遍存在的溶解有机物分子跨越了生物反应谱，而分水岭特有的分子主要是反应性的，很容易转化为二氧化碳。这项研究将在两个特征良好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，另一个在哥斯达黎加的热带常绿森林。水样将在基流和暴雨条件下收集，跨越河流顺序和季节，并使用溪流供水推流式生物反应器将其划分为生物反应类别。样品将用傅里叶变换离子回旋共振质谱仪以及激发发射矩阵的紫外可见吸收光谱和荧光光谱进行分子表征。这项研究的成功完成将提高使用光学传感器了解通过河流网络的碳流动的能力，并促进对溶解有机物的分子性质的理解，这些有机物助长了二氧化碳从溪流和河流向大气的逃逸。

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.