title: Importance of nondiffusive transport for soil CO2efflux in a temperate mountain grassland.
abstract: Soil respiration and its biotic and abiotic drivers have been an important research topic in recent years. While the bulk of these efforts has focused on the emission of CO2from soils, the production and subsequent transport of CO2from soil to atmosphere received far less attention. However, to understand processes underlying emissions of CO2from terrestrial ecosystems, both processes need to be fully evaluated. In this study, we tested to what extent the transport of CO2in a grassland site in the Austrian Alps could be modeled based on the common assumption that diffusion is the main transport mechanism for trace gases in soils. Therefore, we compared the CO2efflux calculated from the soil CO2concentration gradient with the CO2efflux from chamber measurements. We used four commonly used diffusion-driven models for the flux-gradient approach. Models generally underestimated the soil chamber effluxes and their amplitudes, indicating that processes other than diffusion were responsible for the transport of CO2. We further observed that transport rates correlated well with irradiation and, below a soil moisture content of 33%, with wind speed. This suggests that mechanisms such as bulk soil air transport, due to pressure pumping or thermal expansion of soil air due to local surface heating, considerably influence soil CO2transport at this site. Our results suggest that nondiffusive transport may be an important mechanism influencing diel and day-to-day dynamics of soil CO2emissions, leading to a significant mismatch (10-87% depending on the model used) between the two approaches at short time scales.
authors.affiliation: Department of Biology University of Antwerp Wilrijk Belgium.
authors.forename: Marilyn
authors.initials: M
authors.lastname: Roland
authors.affiliation: Department of Biology University of Antwerp Wilrijk Belgium.
authors.forename: Sara
authors.initials: S
authors.lastname: Vicca
authors.affiliation: Institute of Ecology University of Innsbruck Innsbruck Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Bahn
authors.affiliation: Institute of Ecology University of Innsbruck Innsbruck Austria.
authors.forename: Thomas
authors.initials: T
authors.lastname: Ladreiter-Knauss
authors.affiliation: Institute of Ecology University of Innsbruck Innsbruck Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Schmitt
authors.affiliation: Department of Biology University of Antwerp Wilrijk Belgium.
authors.forename: Ivan A
authors.initials: IA
authors.lastname: Janssens
keywords: chamber measurements; diffusion; flux‐gradient approach; pressure pumping; soil CO2 transport; solid‐state sensors