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| Titel |
Non-destructive measurement of carbonic anhydrase activity and the oxygen
isotope composition of soil water |
| VerfasserIn |
Sam Jones, Joana Sauze, Jerome Ogee, Steven Wohl, Alexandre Bosc, Lisa Wingate |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250121898
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| Publikation (Nr.) |
 EGU/EGU2016-787.pdf |
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| Zusammenfassung |
| Carbonic anhydrases are a group of metalloenzymes that catalyse the hydration of aqueous
carbon dioxide (CO2). The expression of carbonic anhydrase by bacteria, archaea and
eukarya has been linked to a variety of important biological processes including pH
regulation, substrate supply and biomineralisation. As oxygen isotopes are exchanged
between CO2 and water during hydration, the presence of carbonic anhydrase in plants and
soil organisms also influences the oxygen isotope budget of atmospheric CO2. Leaf and soil
water pools have distinct oxygen isotope compositions, owing to differences in pool sizes and
evaporation rates, which are imparted on CO2during hydration. These differences
in the isotopic signature of CO2 interacting with leaves and soil can be used to
partition the contribution of photosynthesis and soil respiration to net terrestrial
CO2 exchange. However, this relies on our knowledge of soil carbonic anhydrase
activity and currently, the prevalence and function of these enzymes in soils is poorly
understood.
Isotopic approaches used to estimate soil carbonic anhydrase activity typically involve the
inversion of models describing the oxygen isotope composition of CO2 fluxes to solve for the
apparent, potentially catalysed, rate of oxygen exchange during hydration. This
requires information about the composition of CO2 in isotopic equilibrium with
soil water obtained from destructive, depth-resolved soil water sampling. This can
represent a significant challenge in data collection given the considerable potential
for spatial and temporal variability in the isotopic composition of soil water and
limited a priori information with respect to the appropriate sampling resolution and
depth.
We investigated whether we could circumvent this requirement by constraining carbonic
anhydrase activity and the composition of soil water in isotopic equilibrium with CO2 by
solving simultaneously the mass balance for two soil CO2 steady states differing only in the
oxygen isotope composition of ambient CO2. This non-destructive approach was tested
through laboratory incubations of air-dried soils that were re-wetted with water of known
isotopic composition. Performance was assessed by comparing estimates of the soil water
oxygen isotope composition derived from open chamber flux measurements with those
measured in the irrigation water and soil water extracted following incubations. The influence
of soil pH and bovine carbonic anhydrase additions on these estimates was also
investigated.
Coherent values were found between the soil water composition estimates obtained from
the dual steady state approach and those measured for irrigation waters. Estimates of carbonic
anhydrase activity made using this approach also reflected well artificial increases to the
concentration of carbonic anhydrase and indicated that this activity was sensitive to soil pH. |
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