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| Titel |
{Stable isotope probing of the physical and biological controls that influence the fate and isotopic composition of carbon derived from the terrestrial methane sink } |
| VerfasserIn |
P. J. Maxfield, E. R. C. Hornibrook, N. Dildar, R. P. Evershed |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030853
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| Zusammenfassung |
| Methane oxidizing bacteria (Methanotrophs) occur in every soil order, and are an important
sink for atmospheric CH4 in well aerated soils. The quantity of C cycled via methanotrophic
bacteria in soils is globally significant (Le Mer et al., 2001) yet the fate of methane derived
carbon remains largely unknown and unquantified.
There is generally good agreement regarding the magnitude of the soil CH4 sink
determined by methane flux measurements and process modeling. More poorly characterised
aspects of the soil CH4 sink include: (i) the physical and biological controls that influence the
mechanism of CH4 oxidation in soils; (ii) the fate of oxidized CH4 carbon; (iii) the
proportion of C from CH4 oxidation that is sequestered as organic C or released as CO2 (iv)
the magnitude of kinetic isotope effects (KIEs) associated with high affinity methanotrophy
in soils and the potential influence on the stable carbon isotope composition of atmospheric
CH4.
This research combines multiple stable isotope analytical approaches to investigate the
magnitude, mechanism and pathways of the terrestrial methane sink. Principally 13CH4
stable isotope labeling techniques (Stable isotope probing; SIP) have been used to
characterize and quantify methanotrophic populations in a range of different soils (Maxfield
et al., 2006). Following 13CH4-incubations soil cores were removed for compound-specific C
isotope analyses. Identification and quantification of methanotrophs was effectively achieved
via the analysis of 13C-labelled phospholipid fatty acids (PLFAs) to link bacterial structure
and function. It was also possible to identify the predominant controls influencing the active
methanotrophic populations in both grassland and woodland soils (Maxfield et al.,
2008).
SIP can be combined with further isotopic analyses to facilitate a broader study of
methanotroph C uptake and CH4 derived C sequestration. As SIP facilitates taxonomic
assignments of the soil microorganisms involved in CH4 C cycling, associations can
be made between CH4 derived C, methanotrophic bacteria and the downstream
processing of their biomass C through long-term isotope labeling incubations. The
amount of 13C retained within soils during the latter part of 13CH4 incubations was
monitored through bulk soil δ13C analysis (total sequestered C) and isotopic analysis of
soil biomarkers (C flow pathways). It was apparent that a significant proportion
of the CH4 derived C is retained within soils, as opposed to being lost from the
soil as CO2, despite significant and rapid turnover of C from methanotroph cell
material.
Furthermore, SIP data can be used to evaluate in situ kinetic isotope effects (KIEs)
associated with uptake of atmospheric CH4 by high affinity methanotrophic bacteria with
potential physical and biological factors that influence the mechanism of uptake including
climate, site age, CH4 oxidation rate, microbial biomass, methanotroph population size and
identity. Typically soil high affinity methanotrophy KIEs appear to be largely invariant
between sites. However, in situ KIEs exhibited a statistically significant relationship with
methanotroph biomass and type quantified by 13C stable isotope probing. This finding, albeit
based upon a small dataset, suggests that 13C and 12C partitioning associated with oxidation
of atmospheric CH4 in soil may occur in part as a result of biological as well as
physical processes as suggested by laboratory culturing experiments (Templeton et al.,
2006).
Le Mer J. & Roger P. (2001) Eur. J. Soil Biol. 37: 25-50.
Maxfield, P. J., E. R. C. Hornibrook & R. P. Evershed (2006). Appl. Environ. Microbiol.
72: 3901-
3907.
Maxfield, P. J., E. R. C. Hornibrook & R. P. Evershed (2008). Environ. Microbiol. 10(7):
1917-
1924.
Templeton, A. S.; Chu, K. H.; Alvarez-Cohen, L.; Conrad, M. E. (2006) Geochim.
Cosmochim. Ac., 70, (7), 1739-1752. |
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