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Combining sap flow and eddy covariance approaches to derive stomatal and non-stomatal O3 fluxes in a forest stand |
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| Authors: | AJ Nunn U Metzger R Matyssek |
| Institution: | a Ecophysiology of Plants, Technische Universität München, Am Hochanger 13, D-85354 Freising- Weihenstephan, Germany b Institute for Environment and Sustainability, Joint Research Center, Ispra, Italy c Federal Research and Training Centre for Forests, Natural Hazards and Landscape, Dept. of Alpine Timberline Ecophysiology, Rennweg 1, A - 6020 Innsbruck, Austria |
| Abstract: | Stomatal O3 fluxes to a mixed beech/spruce stand (Fagus sylvatica/Picea abies) in Central Europe were determined using two different approaches. The sap flow technique yielded the tree-level transpiration, whereas the eddy covariance method provided the stand-level evapotranspiration. Both data were then converted into stomatal ozone fluxes, exemplifying this novel concept for July 2007. Sap flow-based stomatal O3 flux was 33% of the total O3 flux, whereas derivation from evapotranspiration rates in combination with the Penman-Monteith algorithm amounted to 47%. In addition to this proportional difference, the sap flow-based assessment yielded lower levels of stomatal O3 flux and reflected stomatal regulation rather than O3 exposure, paralleling the daily courses of canopy conductance for water vapor and eddy covariance-based total stand-level O3 flux. The demonstrated combination of sap flow and eddy covariance approaches supports the development of O3 risk assessment in forests from O3 exposure towards flux-based concepts. |
| Keywords: | Ozone flux Sap flow Eddy covariance Penman-Monteith equation Forests |
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