Enhanced Raman multigas sensing – a novel tool for control and analysis of 13CO2 labeling experiments in environmental research

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.