, Volume 36, Issue 2, pp 153-172

Investigation of the methyl fluoride technique for determining rhizospheric methane oxidation

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Abstract

Methane oxidation rates in the rhizosphere of Pontederia cordata,Sagittaria lancifolia, and Typha latifolia were quantified in fieldstudies using the methyl fluoride inhibition technique. An averageoxidation of 22.9 ± 17.7% (sd,n = 44) was found for all field experiments (oxidation is expressedas a % of total potential emission in the presumedabsence of oxidation). Greenhouse experiments using the same techniquegave an average rhizospheric oxidation of 64.9 ±17.0% (sd, n = 44). Comparison of a subset ofgreenhouse plants with the methyl fluoride (MF) and a light oxic/darkanoxic (LO/DA) technique for suppressing CH4 oxidationyielded similar percentages (57.7 ±15.0% for MF and 58.5 ±13.9% for LO/DA, n = 11). Rhizospheric oxidationdisplayed a seasonal trend in Typha latifolia with decreasingoxidation percentages during warmer months as the importance ofrhizospheric CH4 oxidation declined relative toCH4 emission (46.5 ±13.8% in December and 13.5 ±1.7% in July). However, the absolute rateof methane oxidation was highest during the warmer months (44.2± 3.4 mg m-2 d-1 inDecember and 318.7 ± 151.4 mg m-2d-1 in July). As methane emission rates increased,the sensitivity of the methyl fluoride technique decreased dueto the larger error between replicate flux measurements.