An automated system for trace gas flux measurements from plant foliage and other plant compartments

Plant shoots can act as sources or sinks of trace gases including methane and nitrous oxide. Accurate measurements of these trace gas fluxes require enclosing of shoots in closed non-steady-state chambers. Due to plant physiological activity, this type of enclosure, however, leads to inline-formulaCO₂ depletion in the enclosed air volume, condensation of transpired water, and warming of the enclosures exposed to sunlight, all of which may bias the flux measurements. Here, we present ShoTGa-FluMS (SHOot Trace Gas FLUx Measurement System), a novel measurement system designed for continuous and automated measurements of trace gas and volatile organic compound (VOC) fluxes from plant shoots. The system uses transparent shoot enclosures equipped with Peltier cooling elements and automatically replaces fixated inline-formulaCO₂ and removes transpired water from the enclosure. The system is designed for measuring trace gas fluxes over extended periods, capturing diurnal and seasonal variations, and linking trace gas exchange to plant physiological functioning and environmental drivers. Initial measurements show daytime inline-formulaCH₄ emissions of two pine shoots of 0.056 and 0.089 inline-formulanmol per gram of foliage dry weight (d.w.) per hour or 7.80 and 13.1 inline-formula $M5inlinescrollmathmlunit\mathrm{normal\; nmol}{\mathrm{normal\; m}}^{-\mathrm{normal\; 2}}{\mathrm{normal\; h}}^{-\mathrm{normal\; 1}}$ 64pt13ptsvg-formulamathimg7f446c339092bcc1055b7ea66afb1c05 amt-14-4445-2021-ie00001.svg64pt13ptamt-14-4445-2021-ie00001.png . Simultaneously measured inline-formulaCO₂ uptake rates were 9.2 and 7.6 inline-formula $M7inlinescrollmathmlunit\mathrm{normal\; mmol}{\mathrm{normal\; m}}^{-\mathrm{normal\; 2}}{\mathrm{normal\; h}}^{-\mathrm{normal\; 1}}$ 67pt13ptsvg-formulamathimgac5489fc88cc35e3b1e6d2499112367c amt-14-4445-2021-ie00002.svg67pt13ptamt-14-4445-2021-ie00002.png , and transpiration rates were 1.24 and 0.90 inline-formula $M8inlinescrollmathmlunit\mathrm{normal\; mol}{\mathrm{normal\; m}}^{-\mathrm{normal\; 2}}{\mathrm{normal\; h}}^{-\mathrm{normal\; 1}}$ 58pt13ptsvg-formulamathimg538d5f851d2b3ba575bdefc61140316c amt-14-4445-2021-ie00003.svg58pt13ptamt-14-4445-2021-ie00003.png . Concurrent measurement of VOC emissions demonstrated that potential effects of spectral interferences on inline-formulaCH₄ flux measurements were at least 10-fold smaller than the measured inline-formulaCH₄ fluxes. Overall, this new system solves multiple technical problems that have so far prevented automated plant shoot trace gas flux measurements and holds the potential for providing important new insights into the role of plant foliage in the global inline-formulaCH₄ and inline-formulaN₂O cycles.