Physiological and Molecular Diversity of Atmospheric CH4 Oxidizers in Soil

大气中的CH4对温室效应起着重要的作用，在过去的一个世纪里，由于与农业和工业扩张相关的人类活动，大气中的CH4急剧增加。排水良好的土壤对大气CH4的消耗是大气CH4浓度的重要调节因子。土壤汇的意义不在于其相对于全球CH4收支的大小，而在于其通过对扰动的响应来调节大气CH4长期人为影响的潜力。土壤CH4消耗对土地利用变化（如农业和森林砍伐）非常敏感，也可能对气候变化因素（如干旱或土壤变暖）敏感。由于过去10年土壤中大气CH4的年消耗量与大气CH4的年增加量相当，扰动对土壤CH4汇的累积效应可能对大气中CH4的积累有显著贡献。然而，这一过程的生物学原理尚不清楚，因为研究人员尚未确定哪种类型的土壤细菌实际上在原位氧化大气中的甲烷。本项目将对四个温带和针叶林生态系统中大气CH4氧化剂的生理和分子生态学进行研究，这些生态系统中干扰对土壤CH4消耗的影响已经得到了很好的表征。本研究主要关注以下问题：(1)特定土壤中大气CH4氧化剂的生理特性是什么？(2)在给定的土壤中，什么类型的生物氧化大气中的CH4：甲烷氧化菌还是硝化菌？(3)在给定的土壤中，生态系统类型和干扰制度如何影响哪一类生物是活跃的？许多实验室和现场过程水平的测量，包括CH4饥饿和富集实验、动力学研究和差异抑制剂，将用于获取整个研究地点的微生物群落响应。种型分布和功能基因研究将用于表征研究点内和跨研究点的嗜甲烷和/或硝化菌群落。本研究将估算土壤大气CH4氧化剂的生物多样性，研究这种多样性在自然界中的分布情况，并评估这种多样性在控制土壤CH4消耗对干扰和气候变化的生态系统响应中的重要性。这一策略在科学上是独一无二的，因为它将把现代分子生物学的力量应用于生态系统水平的过程生态学。它将允许对原位过程动力学与微生物群落分子生态学之间的关系进行定性定量检查，从而提高对土壤CH4消耗的生物控制的理解，这仍然是土壤CH4汇最神秘的维度。甲烷氧化是启动这种方法的理想模型，因为它是一种高度专业化的生理学，并且因为在实验室孵育中可以精确控制底物的供应。今后对其他生物地球化学过程的研究将受益于本研究获得的经验。

ABSTRACT STEUDLER (97-08092) Atmospheric CH4 contributes substantially to the greenhouse effect and has increased dramatically in the past century because of human activity associated with agriculture and industrial expansion. Consumption of atmospheric CH4 in well-drained soils is an important regulator of atmospheric CH4 concentration. The significance of the soil sink lies not in its magnitude relative to the global CH4 budget, but rather in its potential to mediate long-term, anthropogenic effects on atmospheric CH4 through its response to disturbance. Soil CH4 consumption is very sensitive to land-use changes, such as agriculture and forest clearcutting, and also may be sensitive to climate change factors, such as drought or soil warming. Because the amount of atmospheric CH4 consumed annually in soil is comparable to the annual increase in atmospheric CH4 over the past decade, the cumulative effects of disturbance on the soil CH4 sink over time could contribute significantly to CH4 accumulation in the atmosphere. However, the biology of this process is poorly understood because researchers have yet to determine what type(s) of soil bacteria actually oxidize atmospheric CH4 in situ. This project will investigate the physiology and molecular ecology of atmospheric CH4 oxidizers in four temperate and taiga forest ecosystems where disturbance effects on soil CH4 consumption have been well characterized. The study focuses on the following questions: (1) What are the physiological characteristics of the atmospheric CH4 oxidizers in a given soil?, (2) What types of organisms oxidize atmospheric CH4 in a given soil: Methanotrophs or Nitrifiers? and (3) How does the ecosystem type and disturbance regime affect which group of organisms is active in a given soil? A number of laboratory and field process-level measurements including CH4 starvation and enrichment experiments, kinetic studies and differential inhibitors will be used to access the microbial community response across the suit e of study sites. Phylotype distribution and functional gene studies will be used to characterize the methanotropic and/or nitrifier communities within and across the study sites. This research will provide an estimate of the biodiversity among soil atmospheric CH4 oxidizers, examine how this diversity is distributed in nature and assess how important this diversity is in controlling the ecosystem-level response of soil CH4 consumption to disturbance and climate change. The strategy is scientifically unique in that it will bring the power of modern molecular biology to bear on ecosystem-level process ecology. It will allow the qualitative quantitative examination of the relationship between in situ process dynamics and the molecular ecology of the microbial community, thus improving understanding of the biological controls over soil CH4 consumption, which remains the most enigmatic dimension of the soil CH4 sink. Methane oxidation is an ideal model for initiating this type of approach because it is a highly specialized physiology, and because substrate supply can be controlled precisely in laboratory incubations. Future investigations on other biogeochemical processes will benefit from experience gained during this research.