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Titel |
Oxic and anoxic mineralization of simple carbon substrates in peat at low temperatures |
VerfasserIn |
Javier Segura, Tobias Sparrman, Mats Nilsson, Jurgen Schleucher, Mats Öquist |
Konferenz |
EGU General Assembly 2016
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 18 (2016) |
Datensatznummer |
250132356
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Publikation (Nr.) |
EGU/EGU2016-12856.pdf |
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Zusammenfassung |
Northern peatlands store approximately one-quarter of the world’s soil carbon and typically
act as net carbon sinks. However a large fraction of the carbon fixed during the growing
season can be emitted back to the atmosphere during winter as CO2 and CH4, despite low
temperatures and frozen conditions, making low temperature biogeochemical processes
crucial for the long-term net ecosystem carbon balance. However, the metabolic processes
driving carbon mineralization under winter conditions are poorly understood and whether or
not peat microbial communities can maintain metabolic activity at temperatures below
freezing is uncertain.
Here we present results from an incubation study aimed at elucidating the potential of peat
microbial communities to mineralize simple carbon substrates to CO2 and CH4 at low
temperatures. Peat samples from the acrotelm were amended with [13C]- glucose and
incubated at -5 ∘C, -3 ∘C, +4 ∘C, and +9 ºC under both oxic and anoxic conditions, and rates
of CO2 and CH4 production were determined. In addition, incorporation of the labelled
substrate into phospholipid fatty acids (PLFAs) were determined to account for
microbial growth during mineralization and the metabolic partitioning between
catabolic and anabolic activity. Biogenic [13C]-CO2 was produced from the added
substrate in peat samples incubated both under oxic and anoxic conditions. Under oxic
conditions the production rates were 3.5, 2.3, 0.3 and 0.07 mg CO2 g SOM−1day−1 at
+9 ∘C, +4 ∘C, -3 ∘C and -5 ∘C, respectively, and corresponding rates for anoxic
conditions were 1.1, 1.0, 0.03 and 0.01 mg CO2 g SOM−1day−1. Consequently the
observed Q10 values of the temperature sensitivity under both oxic and anoxic
conditions increased dramatically upon soil freezing. However, anoxic mineralization
appears less sensitive to temperature as compared to when oxygen is present. Methane
was also produced and detected across the range of the incubation temperatures
in the anoxic incubations, and the impact of freezing was more severe than for
CO2.
The strong reduction in metabolic rates induced by freezing is likely coupled to constraints on
substrate diffusion rates that we can attribute to the reduced liquid water content of the
frozen soil, which exacerbates the observed temperature response. We conclude that
the peat microbial population can remain viable as temperatures drops below the
freezing point of the bulk soil water. Although activity is markedly reduced the
capacity of the microbial population to adapt to harsh winter conditions can have
important implications for the long-term net ecosystem carbon balance of northern
peatlands. |
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