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