Varying atmospheric methane concentrations affect soil methane oxidation rates and methanotroph populations in pasture, an adjacent pine forest, and a landfill
2012
Tate, K.R. | Walcroft, A.S. | Pratt, C.
We describe experiments to better understand how CH₄ oxidation rates by different methanotroph communities respond to changing CH₄ concentrations. We used a novel system of automatically monitored chambers to investigate the response of CH₄ oxidation rates in a New Zealand pasture and adjacent pine forest soil exposed to varying atmospheric CH₄ concentrations. Type II methanotrophs that dominate CH₄ oxidation in the forest soil became progressively saturated as CH₄ concentrations rose from ambient (1.8ppmv) to 570ppmv, as shown by a decrease in uptake efficiency from 20% to 2% removal. By contrast, CH₄ oxidation in the pasture soil where Type I methanotrophs dominate increased in proportion to the increase in CH₄ inlet concentration, oxidising about 2% of the inlet CH₄ flux throughout. Modelling based on Michaelis-Menten kinetics revealed that low-affinity (Type I) methanotrophs were solely responsible for CH₄ oxidation in pasture soils, whereas high affinity (Type II) methanotrophs only contributed about 10% of the CH₄ oxidation in the forest soil. Increased aeration status using a soil–perlite (1:1) mixture doubled CH₄ oxidation rates at both ambient (1.8ppmv) and 40ppmv atmospheric CH₄. A similar volcanic soil previously exposed for 8 y to high CH₄ fluxes from a landfill had removal efficiencies consistently above 95% for atmospheric CH₄ concentrations up to 7500ppmv when the CH₄ oxidation rate was7000μg CH₄ kg⁻¹soil h⁻¹.
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