Combining a Quantum Cascade Laser Spectrometer with an Automated Closed-Chamber System for δ13C Measurements of Forest Soil, Tree Stem and Tree Root CO2 Fluxes
AffiliationUniv Arizona, Dept Ecol & Evolutionary Biol
Keywordsdelta C-13 of forest CO2 fluxes
forest carbon cycling
isotope laser spectroscopy
MetadataShow full item record
CitationBrændholt, Andreas & Ibrom, A & Ambus, Per & Larsen, Klaus & Pilegaard, Kim. (2019). Combining a Quantum Cascade Laser Spectrometer with an Automated Closed-Chamber System for δ13C Measurements of Forest Soil, Tree Stem and Tree Root CO2 Fluxes. Forests. 10. 432. 10.3390/f10050432.
RightsCopyright © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractRecent advances in laser spectroscopy have allowed for real-time measurements of the C-13/C-12 isotopic ratio in CO2, thereby providing new ways to investigate carbon cycling in natural ecosystems. In this study, we combined an Aerodyne quantum cascade laser spectrometer for CO2 isotopes with a LI-COR LI-8100A/8150 automated chamber system to measure the delta C-13 of CO2 during automated closed-chamber measurements. The isotopic composition of the CO2 flux was determined for each chamber measurement by applying the Keeling plot method. We found that the delta C-13 measured by the laser spectrometer was influenced by water vapour and CO2 concentration of the sample air and we developed a method to correct for these effects to yield accurate measurements of delta C-13. Overall, correcting for the CO2 concentration increased the delta C-13 determined from the Keeling plots by 3.4 parts per thousand compared to 2.1 parts per thousand for the water vapour correction. We used the combined system to measure delta C-13 of the CO2 fluxes automatically every two hours from intact soil, trenched soil, tree stems and coarse roots during a two-month campaign in a Danish beech forest. The mean delta C-13 was -29.8 +/- 0.32 parts per thousand for the intact soil plots, which was similar to the mean delta C-13 of -29.8 +/- 1.2 parts per thousand for the trenched soil plots. The lowest delta C-13 was found for the root plots with a mean of -32.6 +/- 0.78 parts per thousand. The mean delta C-13 of the stems was -30.2 +/- 0.74 parts per thousand, similar to the mean delta C-13 of the soil plots. In conclusion, the study showed the potential of using a quantum cascade laser spectrometer to measure delta C-13 of CO2 during automated closed-chamber measurements, thereby allowing for measurements of isotopic ecosystem CO2 fluxes at a high temporal resolution. It also highlighted the importance of proper correction for cross-sensitivity with water vapour and CO2 concentration of the sample air to get accurate measurements of delta C-13.
NoteOpen Access Journal
VersionFinal published version
SponsorsDanish Ministry for Research, Innovation and Higher Education; Danish Council for Independent Research [DFF-1323-00182]