Tracing Low‐CO2 Fluxes in Soil Incubation and 13C Labeling Experiments: A Simplified Gas Sampling System for Respiration and Photosynthesis Measurements

• Published in: Journal of geophysical research. Biogeosciences 2023-09, Vol.128 (9), p.n/a
• Main Authors: Witzgall, K., Hesse, B. D., Seguel, O., Oses, R., Grams, T. E. E., Mueller, C. W.
• Format: Article
• Language: English
• Subjects: Accessibility; Arid lands; Arid zones; Atmosphere; Balloons; biocrust; Biological activity; Carbon cycle; Carbon dioxide; Carbon dioxide concentration; CO2 flux; Compartments; Constraining; Contamination; dryland soil; Fluxes; Gas sampling; heterotrophic soil respiration; Isotope labelling; Isotopic labeling; Labeling; Meteorological balloons; Microorganisms; Mitigation; Photosynthesis; Plant cover; Plants (botany); Pressure effects; Primary production; Radioactive labeling; Respiration; Sampling; Sensitivity; Soil; Soil contamination; Soils; Turnover rate; Uptake; Vegetation; Vegetation cover
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2023JG007410

Quantifying carbon dioxide (CO2) fluxes between soil and atmosphere is key in understanding net ecosystem C exchange and biogeochemical C cycling in plant‐soil systems. In ecosystems with low primary production and sparse vegetation, for example, dry lands or subpolar regions where C fluxes are small, measurement sensitivity is key—even so when measurements are combined with isotopic labeling. Here, we present a simplified gas sampling system developed to facilitate sampling and measurement of low soil CO2 fluxes as well as in situ 13CO2 labeling in the same setup. The capacity of the system was tested in a set of feature tests along with gas measurements of dryland soil‐biocrust systems. The system's sensitivity to capture minor changes in CO2 concentration was confirmed in respiration and photosynthesis measurements of soil‐biocrust systems, where fluxes down to 0.1 μmol CO2 m−2 s−1 were quantified. A balloon, implemented to counterbalance underpressure build‐up during gas withdrawal, mitigated 72% of pressure differences at sampling. The overall system volume was reduced to a minimum to limit contamination caused by residual air, and the design enabled one‐step flushing and evacuation of system compartments and gas sample bags, successfully ruling out cross‐contamination between samples. Ultimately, this system offers a flexible and accessible solution for CO2 measurements that can be applied not only on arid soils with low biological activity and turnover rates, but also on plant‐soil systems. The modifications enabled larger, and thereby more representative, sample volumes to be collected while limiting incubation, contamination, and pressure effects on the intact soil system. Plain Language Summary Measurements of carbon dioxide (CO2) fluxes between soil and atmosphere are crucial to understand the terrestrial carbon cycle. In dry regions, these fluxes are rather small as both the release of CO2 via microbial respiration and uptake of CO2 via photosynthesis is limited by lack of water and sparse vegetation cover. We have developed a simplified CO2 gas sampling setup suitable for incubation experiments of soils with low biological activity and turnover rates, for example, soils from dry lands or subpolar regions, using only cost‐effective, easily available and replaceable system compartments. We tested system parameters in a set of feature tests and could rule out leakage and cross‐contamination. We further confirmed the suitability of the system for