Land-atmosphere carbon monoxide exchange

Carbon monoxide (CO), a trace gas present in the atmosphere at average concentrations of 100 ppb, has an indirect global warming potential due to its critical role in atmospheric chemistry and affects regional air quality. Emission into and uptake from the atmosphere of CO are thus relevant for global climate and regional air quality. Despite these circumstances the global budget of CO, and in particular its land sources and sinks, are still highly uncertain. One major reason for the large uncertainty is a general scarcity of empirical data, many of which date back to the 80ies and 90ies of the 20th century. In addition, available data are confined to ecosystem components, such as leaves, plant or soils, but do not cover the ecosystem scale, which is the relevant scale for assessing whether land ecosystems are sources or sinks for CO. The main aim of the proposed project thus is to (i) reduce the uncertainty of the terrestrial contribution to the CO budget by conducting (probably) the first eddy covariance terrestrial CO flux measurements over a range of representative European ecosystems (grassland, evergreen forests and deciduous forest), yielding the first direct data on the magnitude of ecosystem-scale CO exchange and empirical descriptions of the underlying controls, and (ii) disentangling the above- and below-ground flux contributions to the ecosystem-scale CO exchange by simultaneous measurements of CO exchange through the soil surface in situ along with the ecosystem-scale CO fluxes. In addition, lab-based measurements of microbial CO exchange will be conducted on soil samples from the study sites, testing for the ability of standardised lab methods to relate to differences between study sites determined in the field. The proposed project is designed for a duration of three years and will be conducted in cooperation with four international partners and three partners within the University of Innsbruck.

Carbon monoxide (CO), a trace gas present in the atmosphere at average concentrations of 100 ppb, has an indirect global warming potential due to its critical role in atmospheric chemistry and affects regional air quality. Emission into and uptake from the atmosphere of CO are thus relevant for global climate and regional air quality. Despite these circumstances the global budget of CO, and in particular its land sources and sinks, are still highly uncertain. One major reason for the large uncertainty is a general scarcity of empirical data, many of which date back to the 80ies and 90ies of the 20th century. In addition, available data are confined to ecosystem components, such as leaves, plant or soils, but do not cover the ecosystem scale, which is the relevant scale for assessing whether land ecosystems are sources or sinks for CO. Results from several campaigns in Europe and Asia showed, that natural ecosystem acted as a source for CO during daylight conditions, while fluxes were close to, or around zero during nighttime conditions. Incoming short wave radiation was determined as the most important predictor for CO emissions from these ecosystems. In this regard soils played a major role. In situ measurements as well as lab experiments revealed that soils exposed to UV radiation reduce their sink strength or even act as a source for CO. This effect is even more pronounced if plant litter is available at the site or added to the soil samples. These findings indicate the important role of photo degradation of organic materials as a source for the emission CO from natural ecosystems. Thus, ecosystem with a sparse canopy structure and a high short wave radiative input reaching the soil and/or litter layer are predestined for high CO emissions. These processes are not explicitly represented in current models. Thus, compared with model (MEGAN) results we found a distinct underestimation of natural CO emissions from ecosystems in this model. Furthermore the prescribed positive influence of a high leaf area on CO emissions could not be identified.