It has been known that nitrogenous fertilizers can either stimulate or inhibit methane oxidation in soils.
The mechanism, however, remains unclear. Here we conducted laboratory incubation experiments to
evaluate the effects of ammonium versus nitrate amendment on CH4
oxidation in a rice field soil. The results showed that both N forms stimulated CH4
oxidation. But nitrate stimulated CH4
oxidation to a greater extent than ammonium per unit N base. The 16S rRNA genes and the
pmoA genes were analyzed
to determine the dynamics of total bacterial and methanotrophic populations, respectively. The methanotrophic community consisted of type I and type II methanotrophs and was dominated by type I group after two weeks of incubation. Nitrate promoted both types of methanotrophs, but ammonium promoted
only type I. DNA-based stable isotope probing con
fi
rmed that ammonium stimulated the incorporation
of
13
CH
4
into type I methanotrophs but not type II, while nitrate caused almost homogenous distribution
of
13
CH
4
in type I and type II methanotrophs. Our study suggests that nitrate can promote CH
4
oxidation
more signi
fi
cantly than ammonium and is probably a better N source for both types of methanotrophs in
rice
fi
eld soil. More investigations, e.g. using
15
N labeling, are necessary to elucidate this possibility