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Methane Oxidation and Production Activity in Soils from Natural and Agricultural Ecosystems

^a Dep. of Microbiology, Iowa State Univ., Ames, IA 50011
^b USDA-ARS, National Soil Tilth Lab., 2150 Pammel Drive, Ames, IA 50011

View larger version (30K): [in a new window]   Fig. 1. Methane production potential of soils. Samples were incubated anaerobically with a gas mixture of 75% H2 and 25% CO2. Bars indicate the average rate and error bars indicate the range of the rates (n = 2). M Forest = McFarland Forest, DL Prairie = Doolittle Prairie, RS Prairie = Roadside Prairie, KL Control = Kluever Control, KL Nitrogen = Kluever Nitrogen, KL Broadcast = Kluever Broadcast Manure, KL Inject = Kluever Injected Manure, WC Hill Top = Walnut Creek Hilltop, WC Sideslope = Walnut Creek Sideslope, WC Pothole = Walnut Creek Pothole, DL Farm = Doolittle Farm, RS Farm = Roadside Farm.

View larger version (22K): [in a new window]   Fig. 2. Aerobic methane production. Samples were incubated aerobically with 0.5% CH3F to inhibit CH4 oxidation. Only soils exhibiting CH4 production are shown. Bars indicate the average rate and error bars indicate the range of the rates (n = 2). Symbols are the same as in Fig. 1.

View larger version (31K): [in a new window]   Fig. 3. Methane oxidation under conditions of ambient headspace CH4 concentration. Positive rates indicate gross methane oxidation and negative rates indicate CH4 release. Bars indicate the average rate and error bars indicate the range of the rates (n = 2). Horizontal dashed lines indicate minimum detection limit of ±7.12 pmol CH4 h-1 g-1 for the assay. Symbols are the same as in Fig. 1.

View larger version (34K): [in a new window]   Fig. 4. Methane oxidation assay at elevated headspace methane concentration (1% CH4). Positive rates indicate gross methane oxidation. Bars indicate the average rate and error bars indicate the range of the rates (n = 2). Symbols are the same as in Fig. 1.

View larger version (24K): [in a new window]   Fig. 5. Kinetics of methane oxidation. Curves are the average of two samples. Values in brackets behind the site identification indicate the time (days) for reduction of the initial headspace CH4 concentration by 50% (DT-50). NA indicates no CH4 oxidation activity. Symbols are the same as in Fig. 1.

View larger version (23K): [in a new window]   Fig. 6. Relationship between soil inorganic N concentrations and methane oxidation rates as determined in incubations with ambient headspace CH4 concentrations (A) and elevated headspace CH4 concentrations (1% CH4) (B). McF = McFarland Forest; Dp = Doolittle Prairie; Rp = Roadside Prairie; Kc = Kluever Control; Kn = Kluever Nitrogen; Kb = Kluever Broadcast Manure; Ki = Kluever Injected Manure; Wht = Walnut Creek Hilltop; Wss = Walnut Creek Sideslope; Wph = Walnut Creek Pothole; Df = Doolittle Farm; Rf = Roadside Farm.