Publication Date:
2020-07-10
Description:
Methane emissions from peat bogs are mitigated by methanotrophs, which live in
symbiosis with peat moss (e.g. Sphagnum). Here, we investigate the influence of
temperature and resultant changes in methane fluxes on Sphagnum and methanotroph-
related biomarkers, evaluating their potential as proxies in ancient bogs. A
pulse-chase experiment using 13C-labelled methane in the field clearly showed label
uptake in diploptene, a biomarker for methanotrophs, demonstrating in situ methanotrophic
activity in Sphagnum under natural conditions. Peat cores containing live
Sphagnum were incubated at 5, 10, 15, 20 and 25°C for two months, causing differences
in net methane fluxes. The natural δ13C values of diploptene extracted from
Sphagnum showed a strong correlation with temperature and methane production.
The δ13C values ranged from −34‰ at 5°C to −41‰ at 25°C. These results are best
explained by enhanced expression of the methanotrophic enzymatic isotope effect
at higher methane concentrations. Hence, δ13C values of diploptene, or its diagenetic
products, potentially provide a useful tool to assess methanotrophic activity in past
environments. Increased methane fluxes towards Sphagnum did not affect δ13C values
of bulk Sphagnum and its specific marker, the C23 n-alkane. The concentration of
methanotroph-specific bacteriohopanepolyols (BHPs), aminobacteriohopanetetrol
(aminotetrol, characteristic for type II and to a lesser extent type I methanotrophs)
and aminobacteriohopanepentol (aminopentol, a marker for type I methanotrophs)
showed a non-linear response to increased methane fluxes, with relatively high abundances
at 25°C compared to those at 20°C or below. Aminotetrol was more abundant
than aminopentol, in contrast to similar abundances of aminotetrol and aminopentol
in fresh Sphagnum. This probably indicates that type II methanotrophs became
prevalent under the experimental conditions relative to type I methanotrophs. Even
though BHP concentrations may not directly reflect bacterial activity, they may provide
insight into the presence of different types of methanotrophs.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
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isiRev
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