The link between Soil Methane Oxidation Rate and Abundance of Methanotrophs Estimated by Quantitative PCR

The pmoA gene number is considered as a soil microbiological parameter indicating abundance and potential activity of methanotrophic bacteria. The efficiency of this parameter for prediction and modeling of the real soil methane consumption rates remains an open issue. In the current study rate of methane oxidation by soil at its ambient concentration and the number of the pmoA genes determined by quantitative polymerase chain reaction were compared. Soil samples were collected in May, July, and September 2018 in the middle taiga subzone forest ecosystems near Khanty-Mansiysk, Russia. Soil methane oxidation rate varied from 0.01 to 8 ng СН₄/g dry weight per hour. The pmoA gene numbers per g of dry weight varied from 10⁷ to 10⁹. The correlation between these two parameters became smaller as the scale changed from the soil profile level to ecosystem and interseasonal levels. Methane oxidation rate increased significantly above the threshold methanotroph abundance of 2 × 10⁸pmoA genes/g. Within the intervals below and above this threshold value, no significant changes in methane oxidation rate occurred while methanotroph abundance increased. Thus, quantification of methanotroph abundance alone is insufficient for assessment of methanotrophic activity in upland soils, and the effect of other factors should be considered.