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| Titel |
Using C stable isotopes to infer shifting metabolism in response to variable environmental conditions |
| VerfasserIn |
Ford Ballantyne, Sharon Billings, Christoph Lehmeier, Kyungjin Min |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097047
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| Publikation (Nr.) |
 EGU/EGU2014-12588.pdf |
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| Zusammenfassung |
| The flow of carbon (C) from organic matter substrates through microbial biomass and into
CO2 comprises a complex suite of processes. Organic matter compounds are modified by
extracellular enzyme activity, potentially taken up by microbes, and can either remain as
altered organic compounds in the soil matrix, or are transformed into inorganic C forms,
including CO2. During these transformations, discrimination between 12C and 13C occurs.
The net result of all fractionations is what we observe in the δ13C of respired CO2.
However, our understanding of fractionations associated with soil organic matter (SOM)
transformations is far from complete, especially for biologically-mediated transformations.
To make proper inference from δ13C values of respired CO2, we need a more
comprehensive understanding of what governs isotopic fractionation along the path from
SOM to CO2 release. Here, we present equations for 12C and 13C dynamics in a chemostat
system, with which C flux data coupled to isotopic ratios can be used to infer the degree of
fractionation associated with functionally distinct processes. Using patterns in the
fractionation between substrate and biomass and between biomass and respired CO2
observed for Pseudomonas fluorescens in the experimental chemostat system, we argue
that a single mechanism cannot be responsible for temperature-induced changes
in the flow rates of 12C and 13C from a single substrate, cellobiose, into respired
CO2. We further describe how changing C availability can influence fractionation
among C pools and compare predictions to chemostat runs for which C availability
varied. Our modeling applied to observed C isotope fluxes strongly suggests that
significant discrimination against 13C occurs during cellobiose uptake by P. fluorescens,
and that apparently smooth changes in specific respiration rates and associated
C use efficiency are actually the result of discontinuous shifts in C flow through
anabolic and catabolic pathways. Accounting for such isotopic effects is critical
for a better interpretation of δ13C of soil respiration. Finally, we emphasize that
performing controlled experiments, such as in chemostats, is critical for identifying and
interrogating mechanisms responsible for the genesis of patterns in stable isotopes. |
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