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.
