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Abstract:
Cavity-enhanced Raman multigas spectrometry is introduced as a versatile technique for monitoring of
13CO2 isotope labeling experiments, while simultaneously quantifying the fluxes of O2 and other relevant
gases across a wide range of concentrations. The multigas analysis was performed in a closed cycle; no
gas was consumed, and the gas composition was not altered by the measurement. Isotope labeling of
plant metabolites via photosynthetic uptake of 13CO2 enables the investigation of resource flows in
plants and is now an important tool in ecophysiological studies. In this experiment the 13C labeling of
monoclonal cuttings of Populus trichocarpa was undertaken. The high time resolution of the online
multigas analysis allowed precise control of the pulse labeling and was exploited to calculate the kinetics
of photosynthetic 13CO2 uptake and to extrapolate the exact value of the 13CO2 peak concentration in
the labeling chamber. Further, the leaf dark respiration of immature and mature leaves was analyzed. The
quantification of the photosynthetic O2 production rate as a byproduct of the 13CO2 uptake correlated
with the amount of available light and the leaf area of the plants in the labeling chamber. The ability to
acquire CO2 and O2 respiration rates simultaneously also simplifies the determination of respiratory
quotients (rate of O2 uptake compared to CO2 release) and thus indicates the type of combusted
substrate. By combining quantification of respiration quotients with the tracing of 13C in plants, cavity
enhanced Raman spectroscopy adds a valuable new tool for studies of metabolism at the organismal to ecosystem scale.
