Physical and Biological Controls on the In Situ Kinetic Isotope Effect Associated with Oxidation of Atmospheric CH₄ in Mineral Soils

Abstract

The amounts and delta(13)C values of CH4 at subambient concentrations in soil gas were determined along depth profiles in a U.K. grassland (Bronydd Mawr) and woodland (Leigh Woods). The data were used to determine in situ kinetic isotope effects (KIEs) associated with uptake of atmospheric CH4 by high-affinity methanotrophic bacteria that inha bit soil. Three independent calculation approaches yielded similar mean KIEs of 1.0211 +/- 0.0020 (n=18) for Bronydd Mawr and 1.0219 +/- 0.0010 (n=24) for Leigh Woods. Soil methanotrophy KIEs were largely invariant among oak, beech, and pine forest soils of different ages at Leigh Woods but exhibited a statistically significant relationship with methanotroph biomass in individual plots at Bronydd Mawr and Leigh Woods quantified previously by 13C stable isotope probing. This finding, albeit based upon a small data set suggests that 13C and 12C partitioning associated with the global soil sink for atmospheric CH4 may occur in part as a result of biological as well as physical processes. An accurate assessment of the relative importance of each process to the total KIE requires confirmation that significant partitioning of (13)CH4 and (12)CH4 occurs in pore spaces as a result of differences in diffusion rates.

Substantial high‐affinity methanotroph populations in Andisols effect high rates of atmospheric methane oxidation

“…h −1 . The Ultic Fulvudand CH 4 oxidation rate was higher than any rate observed previously for a range of different mineral soils (Maxfield et al. , 2006; 2008a, b).…”

“…Fig. 1 shows that 13 C‐PLFA concentrations from the Hapludand and the Ultic Fulvudand significantly exceed concentrations observed to date in a range of UK mineral soils ( c. 10‐fold higher) that were incubated under identical conditions (Maxfield et al. , 2006; 2008a, b).…”

“…SIP has also highlighted the low abundance of these difficult to study organisms, which typically comprise <0.01% of total bacteria biomass in mineral soils (Kolb et al. , 2003; Maxfield et al. , 2006; 2008a).…”

“…The SIP of highaffinity methanotrophs in aerobic soils has indicated their relative similarity to known type II low-affinity methanotrophs. SIP has also highlighted the low abundance of these difficult to study organisms, which typically comprise <0.01% of total bacteria biomass in mineral soils (Kolb et al, 2003;Maxfield et al, 2006;2008a).…”

Impact of land management practices on high‐affinity methanotrophic bacterial populations: evidence from long‐term sites at Rothamsted

“… BM = Bronydd Mawr upland grassland; LW = Leigh Woods ancient woodland (Maxfield et al , 2008b); BK, Broadbalk; GeC, Geesecroft; FYM, farmyard manure; N, nitrogen. …”