Collaborative Research: Dimethylsulfide Metabolism in Relation to Carbon Cycling Pathways in Sphagnum-Dominated Wetlands

9632421基尼北部泥炭藓占主导地位的湿地是复杂的、营养不良的生态系统，是大气甲烷的主要来源，并储存了大量的有机碳。这些系统可以向大气中排放异常大量的二甲基硫化物(DMS)，这种排放往往比含有更多硫的海洋栖息地的排放量更大。正在进行的研究表明，DMS的快速通量发生在湿地的营养稀缺地区，而不是在营养较丰富的地点。这一特点可能是由于DMS的产甲烷去甲基化作用不存在于贫营养泥炭中，而发生在微营养泥炭和中性湖泊沉积物中。本研究将调查不同营养状态湿地中DMS的产生、消耗和排放，以阐明末端分解过程在控制DMS释放中的作用。将检验几个假设：1)DMS在湿地的贫养(富营养)地区排放最快，并且这种现象普遍存在；2)DMS在贫养地区排放(和积累)更快，因为DMS不被产甲烷细菌分解；3)化学条件(即pH、矿物质含量)是造成贫养泥炭缺乏DMS消耗的原因4)甲基化甲烷菌在贫养地区稀少5)甲基化硫化物在所有缺氧淡水系统中产生。该项目将结合(1)现场实验测量还原气体的排放和相关化学物种在湿地内营养梯度上的分布，处于不同营养状态的不同湿地；(2)用选定的营养物质和/或微量元素修改湿地地块的田间操作；(3)研究有机物转化途径及其与微量气体生产关系的实验室实验；(4)利用分子生物技术技术调查选定微生物的相对分布和丰度。这些结果将阐明湿地和一般淡水中生产和消费甲基化S化合物的细菌代谢途径的重要方面。由于DMS的转化主要是由位于分解重要末端的微生物进行的，这些数据将提供关于是什么控制了往往积累大量有机物的地点的分解，以及甲烷生成、乙酰化、厌氧代谢以及甲基化和去甲基化活性如何随着营养状态的变化而变化。研究结果将对淡水生态系统具有广泛的适用性。

9632421 Kiene Northern Sphagnum-dominated wetlands are complex, nutrient-poor ecosystems that are major sources of atmospheric methane and store tremendous quantities of organic carbon. These systems can emit unusually large amounts of dimethylsulfide (DMS) into the atmosphere, and this efflux is often greater than emissions from marine habitats that contain much more sulfur. Ongoing studies revealed that rapid fluxes of DMS occur in oligotrophic areas of wetlands rather that in more nutrient-rich sites. This peculiarity may to be due to the fact that the methanogenic demethylation of DMS does not occur in oligotrophic peats, while it does in minerotrophic ones and in neutral lake sediment. The present study will investigate the production, consumption and emission of DMS in wetlands of varying trophic status to elucidate the role of terminal decomposi~ processes in controlling DMS release. Several hypotheses will be tested: 1) DMS emissions are most rapid in oligotrophic (ombrotrophic) regions of wetlands, and this phenomenon is ubiquitous 2) DMS emissions (and accumulation) are faster in oligotrophic regions because DMS is not decomposed by methanogenic bacteria 3) Chemical conditions (i.e., pH, mineral content) are responsible for the lack of DMS consumption in oligotrophic peats 4) Methylotrophic methanogens are sparse in oligotrophic areas 5) Methylated sulfides are produced in all anoxic freshwater systems The project will combine (1) field experiments measuring emissions of reduced gases and distribution of pertinent chemical species along trophic gradients within a wetland, and in separate wetlands of different trophic status; (2) field manipulations in which wetland plots will be amended with selected nutrients and/or trace elements; (3) laboratory experiments to investigate pathways of organic matter transformations and relationships with trace gas production; (4) investigations of the relative distribution and abundance of selected microorganisms using molecular biotechno logy techniques. The results will elucidate important aspects of bacterial metabolic pathways for the production and consumption of methylated S compounds in wetlands, and freshwaters in general. Since DMS transformations are conducted primarily by microorganisms situated at the important terminal end of decomposition, these data will provide insights into what controls decomposition in sites that tend to accumulate large quantities of organic matter, and how methanogenesis, acetogenesis, anaerobic metabolism, and methylation and demethylation activity vary in response to changes in trophic status. The results will have broad applicability to freshwater ecosystems in general.