HR: 09:30h
AN: B41G-07    [Abstracts]
TI: A coupled molecular and field-based approach to study microbial controls on methane flux in upland soils
AU: * Judd, C R
EM: Craig.Judd@colostate.edu
AF: Department of Biology and Graduate degree program in Ecology, Colorado State University, Fort Collins, CO 80521,
AU: von Fischer, J C
EM: jcvf@colostate.edu
AF: Department of Biology and Graduate degree program in Ecology, Colorado State University, Fort Collins, CO 80521,
AU: Fierer, N
EM: fierer@cires.colorado.edu
AF: Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309,
AB: Predicting the responses of ecosystems to global change depends, in part, on understanding how soil microbial communities respond to external controls. To address this question, we are studying a relatively simple biogeochemical process: methane consumption in upland (i.e., well-drained, oxic) soils. In this process, methane molecules diffuse from the atmosphere into the soil, where they are consumed by methanotrophic bacteria. Because of the simplicity of this process, we have been able to develop a reaction-diffusion model that allows us to directly quantify methanotroph activity in situ from chamber-based measures of flux and diffusivity. Moreover, because the bacteria that oxidize methane come from a phylogenetically cohesive group, we can use molecular tools to quantify the size of methanotroph community and determine its species composition. Our application of these approaches on the Shortgrass Steppe Long-Term Ecological Research (SGS LTER) site in northeastern Colorado has revealed strong temporal and spatial patterns in methane uptake rates that are driven primarily by methanotroph activity, and very little by soil diffusivity. The temporal patterns in methanotroph activity follow seasonal changes in soil temperature and water content, with sharp reductions in activity associated with hot, dry conditions. Spatial patterns in activity follow differences in soil texture, with sandier soils expressing a greater range of methanotroph activity than clay soils. Although methanotroph abundances did not vary across soil types, the phylogenetic structure of the methanotroph communities differed significantly between clay and sand soil types. In addition, we found that the majority of methanotrophs were not the usual Type I or Type II, but instead were of the JR2 and JR3 types previously found only in a dry California grassland by Horz et al. AEM (2005). Together, these observations suggest that the species composition of methanotroph communities reflects changes in the physical environment. Given the potential for specialization among methanotrophs (e.g., for desiccation tolerance, or for methane affinity), we anticipate that the specific phylogenetic and physiological characteristics of methane oxidizer communities will modulate the responses of upland methane fluxes to climate change.
DE: 0412 Biogeochemical kinetics and reaction modeling (0414, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: 2007 Fall Meeting