the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A multiplexing system for quantifying oxygen fractionation factors in closed chambers
Abstract. The study of isotopic ratios of atmospheric oxygen in fossilized air trapped in ice core bubbles provides information on variations in the hydrological cycle at low latitudes and productivity in the past. However, to refine these interpretations, it is necessary to better quantify fractionation of oxygen in the biological processes such as photosynthesis and respiration. We set up a system of closed biological chambers in which we studied the evolution of elemental and isotopic composition of O2 due to biological processes. To easily replicate experiments, we developed a multiplexing system which we describe here. We compared measurements of elemental and isotopic composition of O2 using two different measurement techniques: optical spectrometry (Optical-Feedback Cavity- Enhanced Absorption Spectroscopy, i.e. OF-CEAS technique), which enables higher temporal resolution and continuous data collection and isotopic ratio mass spectrometry (IRMS) with a flanged air recovery system, thus validating the data analysis conducted through the OF-CEAS technique. As a first application, we investigated isotopic discrimination during respiration and photosynthesis. We conducted a 5-day experiment using maize (Zea mays L.) as model species. The 18O discrimination value for maize during dark plant respiration was determined as - 17.8 ± 0.9 ‰ by IRMS and - 16.1 ± 1.1 ‰ by optical spectrometer. We also found a value attributed to the isotopic discrimination of terrestrial photosynthesis equal to + 3.2 ± 2.6 ‰ by IRMS and + 6.7 ± 3.8 ‰ by optical spectrometer. These findings were consistent with a previous study by Paul et al. (2023).
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Status: open (until 12 Nov 2024)
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RC1: 'Comment on egusphere-2024-1755- attached in file', Anonymous Referee #1, 01 Sep 2024
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This manuscript by Paul et al. is a methods development paper primarily. It describes the development of a multiplexing system and the application of two different analytical techniques – Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) and Isotope Ratio Mass Spectrometry (IRMS) – to determine the elemental and isotopic composition of O2 produced by biological processes occurring in a closed chamber. Using OF-CEAS for O2 isotope measurement is a relatively novel idea and Paul et al. effectively demonstrate its capability in this work.
The methods section is very well written in this work and would enable readers to recreate this experimental design.
A few minor comments on the work are highlighted below:
- Line 91 -92: A sentence explaining how d18O is used to reconstruct oceanic vs terrestrial productivity would be helpful.
- Line 105: Replace “despite our system...” with “although our system...”
- Line 108-121: Adding a sentence explaining what overall factors are considered when choosing type of species for experimental setup would be helpful
- Line 236: ‘reference’ is highlighted, citation missing
- Line 292: “Experimental problem:. Please describe what the experimental problem was. Since this is a new method and would potentially be adopted by other labs, it would be useful to know what the problem was and how it was addressed.
- Line 341: Explain why maize was chosen as the preferred option
- Figures: Adding shaded error bars/ or some sort of way to indicate uncertainty in regression slopes would be visually helpful.
Citation: https://doi.org/10.5194/egusphere-2024-1755-RC1 -
EC1: 'Reply on RC1', Ciro Apollonio, 17 Sep 2024
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Citation: https://doi.org/
10.5194/egusphere-2024-1755-EC1
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