Collaborative Research: Acetate Biogeochemistry in Northern Wetlands: Implications for Methane Formation During Climate Change

摘要北方湿地储存了大量的碳，是大气甲烷的重要来源。迫在眉睫的气候变化可能会极大地影响这些环境在碳循环中的作用。有机物的分解在这些湿地中以厌氧方式进行。然而，最近的研究结果表明，终端产甲烷步骤在北方湿地改变相对于更南部的系统，乙酸作为终端产品，即使甲烷生产继续通过氢利用。如果这种现象是普遍存在的，那么乙酸盐不是北方湿地中的重要中间体，而是作为分解的最终产物;最终有氧降解为CO2而不是甲烷。北方湿地中乙酸盐的积累代表了我们对厌氧分解理解的一种范式转变。北部的变暖可能会使这一过程转向更南部的湿地。如果是这样的话，那么北部的甲烷产量将大大增加，可能会发生从单独的warming.This工作将测试的假设，即北方湿地不支持显着的甲烷从乙酸盐和乙酸盐的形成和积累是一个重要的终端步骤，在有机物厌氧降解。一个多学科小组正在对这一现象进行调查，该小组将利用实地和实验室调查以及微生物、分子生物学、地球化学、土壤学和稳定同位素方法。1）通过检查乙酸盐浓度和生产率，地球化学条件，以及对代表主要的环极北极、亚北极和北方北方环境的各种北方湿地类型应用同位素和分子技术; 2）通过进行季节性研究，为确定产甲烷途径和乙酸循环控制的变化提供时间框架; 3）利用实验室对培养条件的操作来确定物理和化学参数对最终分解的影响; 4）确定与其他湿地和其他厌氧生境相比，细菌种群是否不同。培养试验，放射性示踪分析，稳定同位素和天然放射性碳丰度将用于在实地和实验室实验中研究分解途径。通过PCR-DGGE和杂交探针等分子生物学手段，研究了该湿地中细菌的多样性和种群结构。结果表明，该湿地甲烷形成的生物化学途径与南方湿地相比具有独特性，这对我们预测该湿地在向全球大气排放甲烷和降解碳储存方面的作用具有重要意义。乙酸盐可以作为主要的有机终产物，因此其将构成与甲烷生成同时发生的单独的末端分解途径。这里提出的多学科研究将描绘这些过程的重要细节，并将有助于展示其空间意义。

AbstractNorthern wetlands store large quantities of carbon and are significant sources of atmospheric methane. Impending climatic changes may greatly affect the role of these environments in the carbon cycle. Decomposition of organic matter occurs anaerobically in these wetlands. However, recent findings suggest that the terminal methanogenic step in northern wetlands is altered relative to more southerly systems, with acetate acting as a terminal product even though methane production continues via hydrogen utilization. If this phenomenon is ubiquitous, then acetate is not a significant intermediate in northern wetlands, but serves as a terminal product of decomposition; one that is ultimately degraded aerobically to CO2 rather than methane. Acetate accumulation in northern wetlands represents a paradigm shift in our understanding of anaerobic decomposition. It is possible that warming in the north will shift this process toward what occurs in more southerly wetlands. If so, then methane production in the north will increase greatly over what might occur from warming alone.This work will test the hypothesis that northern wetlands do not support significant methanogenesis from acetate and that acetate formation and accumulation is an important terminal step during anaerobic degradation of organic matter. This phenomenon is being investigated by a multidisciplinary team that will utilize field and laboratory investigations and microbiological, molecular biology, geochemical, pedological, and stable isotope approaches.The objectives of the project are: 1) assess the ubiquity of the acetate-accumulating phenomenon by examining acetate concentrations and production rates, geochemical conditions, and by applying isotopic and molecular techniques to a variety of northern wetland types representative of the major circumpolar arctic, subarctic and northern boreal environments; 2) Provide a temporal framework for determining variations in controls on methanogenic pathways and acetate cycling by conducting seasonal studies; 3) determine the effects of physical and chemical parameters on terminal decomposition using laboratory manipulations of incubation conditions; 4) determine if the bacterial populations are distinct compared to other wetlands and other anaerobic habitats.Incubation assays, radiotracer analyses, stable isotopes and natural radiocarbon abundances will be used to address pathways of decomposition in field and laboratory experiments. Molecular approaches including PCR-DGGE and hybridization probing will be used to determine bacterial diversity and population structure.A demonstration that biochemical pathways of methane formation in these wetlands are unique compared to their more southerly counterparts, has tremendous implications for our ability to predict the what the role of these wetlands will be in contributing methane to the global atmosphere and in their ability to degrade stored carbon. Acetate may serve as a primary organic end product, which would thus constitute a separate terminal decomposition pathway occurring simultaneously with methanogenesis. The multi-disciplinary study proposed here will delineate the important details of these processes and will serve to demonstrate their spatial significance.