Control of methane and carbon dioxide emissions by sulfur biogeochemistry in terrestrial ecosystems
EMSL Project ID
48923
Abstract
Freshwater wetlands are responsible for 40% of the methane emissions worldwide. Despite very low amounts of ambient sulfate, these ecosystems often support high rates of sulfate reduction, rivaling even those measured in ocean sediments. Because sulfate reduction is more energy efficient than methanogenesis, sulfate reducers often outcompete methanogens for resources. Thus sulfate reduction represents a control point for the emission of the strong greenhouse gasses methane and carbon dioxide. We propose to examine wetland soils that are likely to change water regimes as global warming progresses– boreal forest tundra soils from central Alaska and soils from a gradient of snow-dominated to rain-dominated hydrologic regimes from the Oregon Cascades. We propose using mesocosm cores obtained from these environments as experimental units. The cores will be conditioned and subjected to varying moisture regimes. We will develop a rapid sulfur 3-isotope analysis protocol using NanoSIMS to identify microenvironments predominated by sulfate reduction and sulfur disproportionation and use these analyses to inform sampling protocols for metagenomic, metaproteomic, and metalipidomic analyses. Using sulfur 3-isotope analyses, we will test the hypothesis that sulfate reducing metabolism will predominate in anaerobic microsites and sulfur disproportionating metabolisms will predominate in microsites with fluctuating moisture regimes. Relative amounts of methane and carbon dioxide emissions from replicate cores of these soils will be correlated to sulfate reduction rates obtained from 35S sulfate tracer studies performed at the EMSL Radiological Annex. T-RFLP analyses will be used for presumptive identification of active populations and 13C labeling of simple substrates will allow stable isotope probing of the metaproteome and metalipidome. We will test the hypothesis that the metagenome will be the same between sulfate reducing and disproportionating microenvironments, but that the metaproteome and metalipidome will change. Using bulk sulfate reduction rates in conjunction with measured methane and carbon dioxide fluxes, we will test the hypothesis that methane production will be inversely correlated with sulfate reduction rates.We believe that PNNL and EMSL are the only place where these measurements could all be made. The combination of world class mass spectrometric instrumentation and expertise, as well as the ability to carry out parallel geochemical analyses using radio isotopes precludes other laboratories.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2015-10-01
End Date
2017-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members