Response of methanotrophic activity in forest soil to methane availability

Deprivation of methane did not affect the capacity of forest soils to consume atmospheric methane. Methane consumption by intact soil cores that had been deprived of methane for 75 days was similar to that by cores that had been incubated under ambient air. However, seasonal differences in the stability of atmospheric methane consumption were observed. The capacity of soils collected during relatively dry periods (soil water contents 14–40%) to oxidize methane decreased over 24 days in both the presence and absence of atmospheric methane. In contrast, methane consumption by soils collected during a comparatively wet period (soil water contents >50%) remained constant. The rate of methane oxidation increased with increasing methane concentrations to a maximum of 1.0 nmol h−1 gdw soil−1; the apparent Km for methane uptake was 10 nM. Incubation of soils with 160 or 1000 ppm methane for up to 7 weeks did not increase their capacity to oxidize atmospheric methane, even though the capacity for methane oxidation at higher methane concentrations increased. These results collectively suggest that the response to methane deprivation may involve utilization of other substrates, and that the growth of bacteria that oxidize atmospheric methane is constrained by factors other than methane availability.