25th International Meeting on Organic Geochemistry IMOG 2011

O-29
Influence of temperature on methane cycling and methanotrophrelated
biomarkers in peat moss
Julia van Winden 1 , Gert-Jan Reichart 1 , Helen Talbot 2 , Niall McNamara 3 , Albert Benthien 4 ,
Jaap Sinninghe Damsté 1,5
1 Utrecht University, Utrecht, Netherlands, 2 Newcastle University, Newcastle, United Kingdom, 3 CEH,
Lancaster, United Kingdom, 4 AWI, Bremerhaven, Germany, 5 NIOZ, Texel, Netherlands (corresponding
author:j.vanwinden@geo.uu.nl)
Peat bogs are the largest terrestrial carbon sink and
an important source for atmospheric methane.
Methane emissions from peat bogs are, however,
reduced by symbiotic methane oxidizing bacteria
(methanotrophs), which live in association with peat
moss (Sphagnum). Future climate change projections
indicate that mid to high latitudes, especially Western
Siberia, with the largest peat bog occurrence globally,
may become increasingly wetter and warmer.
According to reaction kinetics, increasing
temperatures will enhance both biological methane
production as well as methane oxidation. It is,
however, impossible to a priori predict which process
will outcompete the other.
To unravel the effect of temperature on both methane
production and oxidation, intact peat cores containing
actively growing Sphagnum were incubated at 5, 10,
15, 20 and 25 ºC. Even though methane consumption
increased with increasing temperature, methanotrophs
were not able to compensate for the increased
methane production by methanogens. Moreover, the
efficiency of the Sphagnum-methanotroph consortium
as a filter for methane escape strongly decreased with
increasing temperature (Fig. 1).
Fig. 1. Methane retention [%] versus temperature
How temperature-related changes have affected
methane cycling in peat bogs in the past can be
studied by examining ancient peat cores. To resolve
the effect of temperature and methane cycling on
potential methanotroph proxies, Sphagnum mosses
grown during this mesocosm study were analyzed for
intact bacteriohopanepolyols (BHPs) and compound
specific carbon isotopes of hopanoids.
Aminobacteriohopanepentol (aminopentol) is a
marker for type I methanotrophs, while
aminobacteriohopanetetrol (aminotetrol) is produced
by type II methanotrophs, and to a lesser extent by
type I methanotrophs. These methanotroph BHPs
increased slightly with increasing temperature, with
especially high concentrations at 25 ºC. However, due
to the limited duration of the experiment it was, not
possible to show a direct relationship with methane
cycling. Aminotetrol was significantly more abundant
than aminopentol, particularly at higher temperatures,
indicating that type II methanotrophs more easily
adapt to changing environmental conditions
compared to type I methanotrophs.
Diploptene is a bacterial marker which is produced by,
but not exclusive to, methanotrophs. Compoundspecific
δ 13 C values of diploptene demonstrated a
strong decrease with increasing temperature, with
values of -33,9‰ at 5 ºC and -40,7‰ at 25 ºC. This
relationship is best explained by enhanced methane
cycling at higher temperatures, caused by increased
methanotroph abundance and/or enhanced isotopic
fractionation as a result of increased methane
availability.
Our study shows that extent of methane retention by
symbiotic methanotrophs in peat bogs decreases with
increasing temperature. Furthermore, a combination
of BHPs and δ 13 C values of diploptene, or its
diagenetic products, potentially provide powerful tools
to assess methanotrophic community structures and
methanotrophic activity, also in past environments.
88