Tracing Low‐CO2Fluxes in Soil Incubation and 13C Labeling Experiments: A Simplified Gas Sampling System for Respiration and Photosynthesis Measurements

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 CO2fluxes as well as in situ 13CO2labeling 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 CO2concentration was confirmed in respiration and photosynthesis measurements of soil‐biocrust systems, where fluxes down to 0.1 μmol CO2m−2s−1were 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 CO2measurements 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. 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 CO2via microbial respiration and uptake of CO2via photosynthesis is limited by lack of water and sparse vegetation cover. We have developed a simplified CO2gas 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 capturing small CO2fluxes in photosynthesis and respiration measurements of soils with biocrusts. A balloon was installed to counterbalance pressure build‐up during sampling, allowing for larger gas volumes to be collected, which resulted in a mitigation of 72% of the underpressure build‐up. This system offers a straightforward and accessible solution for CO2measurements, with features limiting contamination and pressure effects on the research sample. We present a simplified and low‐cost gas sampling system, developed for quantifying CO2fluxes in soil incubation experimentsRespiration rates down to 0.1 μmol CO2m−2s−1were quantified, confirming the suitability of the system for low‐CO2flux measurementsA balloon was installed, mitigating 72% of pressure changes in the headspace during sampling We present a simplified and low‐cost gas sampling system, developed for quantifying CO2fluxes in soil incubation experiments Respiration rates down to 0.1 μmol CO2m−2s−1were quantified, confirming the suitability of the system for low‐CO2flux measurements A balloon was installed, mitigating 72% of pressure changes in the headspace during sampling