D. Kightley et al., CAPACITY FOR METHANE OXIDATION IN LANDFILL COVER SOILS MEASURED IN LABORATORY-SCALE SOIL MICROCOSMS, Applied and environmental microbiology, 61(2), 1995, pp. 592-601
Laboratory-scale soil microcosms containing different soils were perme
ated with CH4 for up to 6 months to investigate their capacity to deve
lop a methanotrophic community. Methane emissions were monitored conti
nuously until steady states were established. The porous, coarse sand
soil developed the greatest methanotrophic capacity (10.4 mol of CH4.m
(-2).day(-1)), the greatest yet reported in the literature. Vertical p
rofiles of O-2, CH4, and methanotrophic potential in the soils were de
termined at steady state. Methane oxidation potentials were greatest w
here the vertical profiles of O-2, and CH4 overlapped. A significant i
ncrease in the organic matter content of the soil, presumably derived
from methanotroph biomass, occurred where CH4 oxidation was greatest.
Methane oxidation kinetics showed that a soil community with a low met
hanotrophic capacity (V-max of 258 nmol.g of soil(-1).h(-1)) but relat
ively high affinity (k(app) of 1.6 mu M) remained in N-2-purged contro
l microcosms, even after 6 months without CH4. We attribute this to a
facultative, possibly mixotrophic, methanotrophic microbial community.
When purged with CH4, a different methanotrophic community developed
which had a lower affinity (k(app) of 31.7 mu M) for CH4 but a greater
capacity (V-max of 998 nmol.g of soil(-1) h(-1)) for CH4 oxidation, r
eflecting the enrichment of an active high-capacity methanotrophic com
munity. Compared with the unamended control soil, amendment of the coa
rse sand with sewage sludge enhanced CH4 oxidation capacity by 26%; K2
HPO4 amendment had no significant elfect, while amendment with NH4NO3
reduced the CH4 oxidation capacity by 64%. In vitro experiments sugges
ted that NH4NO3 additions (10 and 71 mu mol.g of soil(-1)) inhibited C
H4 oxidation by a nonspecific ionic effect rather than by specific inh
ibition by NH4+.