High-resolution, ecosystem-level CO2, H2O and CH4 fluxes with novel automatic light/dark chamber.

The eddy covariance measurement technique is broadly applied in terrestrial ecosystems forecosystem-level measurements of CO2, CH4 and H2O exchange between ecosystem andatmosphere. However, in ecological experiments with smaller plot sizes than typicalfootprints of eddy covariance towers, such as in field-scale climate change experiments, theeddy covariance technique cannot be applied. In these experiments, measurements of gasexchange with the atmosphere rely on chamber techniques. However, chamberslarge enough to measure at the ecosystem scale are currently not commerciallyavailable.We built a novel automatic chamber for measurement of gas fluxes at the ecosystemscale in short-stature ecosystems. The chamber covers an area of 2827 cm2 (60cm diameter), is 80 cm tall (volume: 225 L). The unique feature of the chamberis that it is capable of switching automatically between light and darkened modeenabling separation of light-sensitive and light-indifferent processes. For CO2 fluxes,net exchange (NEE) is measured in the light mode, while ecosystem respiration(RE) is measured in the darkened mode and Gross Primary Productivity (GPP) isestimated as NEE – RE. The chamber is controlled by a LI-COR 8100/8150 multiplexersystem.We measured hourly fluxes of CO2, H2O and CH4 continuously for 3 years in DanishCalluna vulgaris (common heather) heathland thus generating more than 40,000 individualchamber measurements. We will present an analysis of the novel, high-frequency data setincluding new insights into the diel fluctuation in RE rates in response to diel, weeklyand seasonal changes in GPP, temperature, soil water availability and rain events.Novel findings include the observation of increased RE at similar temperaturesduring daytime compared to nighttime, thus questioning if RE during daytime can beestimated based on temperature responses from nighttime NEE measurements. Over thestudy period the ecosystem was a net sink for both CO2 and CH4. Finally, we alsoestimated the evapotranspiration rates of the ecosystems by fitting non-linear modelsto the H2O concentration development inside the chamber. The presentation willdiscuss the potential of using closed chambers for estimating evapotranspirationin experiments with plot sizes too small for application of the eddy-covariancetechnique. In summary, the ability of the chamber to be both transparent and darkenedenables high-frequency, direct measurements of the processes of photosynthesisand ecosystem respiration during daytime. This is an advancement compared totransparent-only chambers as well as the eddy covariance technique which bothrely on modelling daytime GPP and RE from the NEE measurements obtained. [ABSTRACT FROM AUTHOR]