Singlet Oxygen's Role in the Photochemical-Biochemical Degradation of Dissolved Organic Carbon

溶解有机物(DOM)是水生生态系统中最大的有机碳库，是全球碳循环的重要环节。尽管每年有大量陆源DOM(约2x1014克)流入海洋，但这种物质几乎没有积累，这表明它正在迅速分解。虽然光化学和生化降解这两个主要的损失已经得到了很好的研究，但很少有人研究导致降解和化学转化的机制，特别是关于光化学过程。在这项研究项目中，明尼苏达大学双城分校的研究人员将调查活性氧物种(ROS)对天然水体中有机物的化学组成、反应活性和生物有效性的影响。本项目将以苏必利尔湖为研究地点，目标是：(1)表征DOM暴露在1O2下的化学和光学性质的变化；(2)确定DOM与1O2反应后的稳定性和营养品质的变化；(3)研究1o2反应性氨基酸-组氨酸、色氨酸、蛋氨酸、半胱氨酸和酪氨酸-及其1o2反应产物的微生物利用差异，以及(4)量化苏必利尔湖的1o2产生率。为了实现这些目标，来自两个来源(土壤和浮游植物)以及沿时空梯度(河流和近海)的DOM将受到多种处理，包括阳光和明确的1o2来源(存在和不存在灭绝剂)。这项研究的特点是使用非光化学的1O2源，这将使人们能够独立于阳光检查1O2的影响。将通过生物测定和化学分析来观察对DOM稳定性和化学结构的影响。在氧化DOM存在的情况下，由于1O2与DOM中存在的特定氨基酸发生反应而导致微生物生长效率下降的假设将得到检验。这项研究有望首次证明，当DOM暴露在阳光下时，单线态氧是否导致了DOM生物利用度的许多变化。它还将首次测量大型水生系统中的单线态氧浓度。就更广泛的影响而言，可以肯定的是，微生物和光化学过程在环境生物地球化学中发挥着核心作用。该项目中研究的过程将有助于理解全球动态，如碳循环、营养限制和富营养化。这个项目将支持一名年轻的研究人员(麦克尼尔)，并由一名生态学家和一名化学家合作完成。此外，拟议项目中的几项活动将促进教学和培训目标，包括：对本科生和研究生以及K-12教师进行培训和教育。PIs将参加针对少数族裔学生的夏季本科生研究计划(通过生物科学学院LSSURP计划)。PIs还将参加以淡水生态为重点的K-12教师培训计划。此外，该项目将与明尼苏达大学的NSF-RSEC项目相联系，通过促进其中一名研究人员和一名主要本科机构的教员之间的现有合作。

ABSTRACTOCE-0527196Dissolved organic matter (DOM) is the largest pool of organic carbon in aquatic ecosystems and constitutes a vital link in the global carbon cycle. Despite a large flux (ca. 2 x 1014g) of terrigenous DOM into the oceans every year, little of this material accumulates suggesting that it is rapidly decomposed. While the two main losses, photochemical and biochemical degradation, have been well studied, little work has examined the mechanisms responsible for degradation and chemical transformations, especially regarding photochemical processes.In this research project, researchers at the University of Minnesota - Twin Cities will investigate the effects of a reactive oxygen species (ROS), singlet oxygen (1O2), on the chemical composition, reactivity and bioavailability of organic matter in natural waters. This project will use Lake Superior as a study site and the goals are: (1) To characterize the changes to the chemical and optical properties of DOM when exposed to 1O2; (2) To determine the changes in lability and nutritive quality of DOM following reaction with 1O2; (3) To examine the differential microbial utilization of 1O2-reactive amino acids-histidine, tryptophan, methionine, cysteine, and tyrosine-and their 1O2 reaction products, and (4) To quantify 1O2 production rates in Lake Superior.To achieve these goals, DOM from two sources (soil and phytoplankton) and along a temporal-spatial gradient (river and offshore) will be exposed to a number of treatments including sunlight and well-defined sources of 1O2 with and without quenchers present. This study features the use of non-photochemical 1O2 sources that will enable examination of effects of 1O2 independent of sunlight. Effects on lability and chemical structure of DOM will be observed via bioassays and chemical analyses. The hypothesis that decreased microbial growth efficiency is observed in the presence of oxidized DOM, due to the reaction of 1O2 with specific amino acids present in DOM will be tested. This study is expected to be the first to demonstrate whether or not singlet oxygen is responsible for many of the changes in DOM bioavailability when it is exposed to sunlight. It will also produce some of the first measurements of singlet oxygen concentrations in large aquatic systems.In terms of broader impacts, it ic certain that microbes and photochemical processes play a central role in environmental biogeochemistry. The processes examined in this project will facilitate understanding of global dynamics such as the carbon cycle, nutrient limitation and eutrophication. This project will support a young investigator (McNeill) and is collaboration between an ecologist and a chemist. In addition, several activities in the proposed project will promote teaching and training goals including: training and education of undergraduate students and graduate students and K-12 teachers. The PIs will participate in summer undergraduate research programs directed toward minority students (through the College of Biological Sciences LSSURP Program). The PIs will also participate in a K-12 teacher-training program focused on freshwater ecology. Additionally, this project will link with the NSF-RSEC program at the University of Minnesota by fostering an existing collaboration between one of the investigators and a faculty member at a Principally Undergraduate Institution.