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 CH
4
oxidation in a rice
fi
eld soil. The
results showed that both N forms stimulated CH
4
oxidation. But nitrate stimulated CH
4
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 meth-
anotrophic 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
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 toevaluate the effects of ammonium versus nitrate amendment on CH4oxidation in a ricefield soil. Theresults showed that both N forms stimulated CH4oxidation. But nitrate stimulated CH4oxidation to agreater extent than ammonium per unit N base. The 16S rRNA genes and thepmoAgenes were analyzedto determine the dynamics of total bacterial and methanotrophic populations, respectively. The meth-anotrophic community consisted of type I and type II methanotrophs and was dominated by type I groupafter two weeks of incubation. Nitrate promoted both types of methanotrophs, but ammonium promotedonly type I. DNA-based stable isotope probing confirmed that ammonium stimulated the incorporationof13CH4into type I methanotrophs but not type II, while nitrate caused almost homogenous distributionof13CH4in type I and type II methanotrophs. Our study suggests that nitrate can promote CH4oxidationmore significantly than ammonium and is probably a better N source for both types of methanotrophs inricefield soil. More investigations, e.g. using15N labeling, are necessary to elucidate this possibility
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