Combining sap flow and eddy covariance approaches to derive stomatal and non-stomatal O3 fluxes in a forest stand

Amsterdam

Elsevier

2010

S. 2014-2022

SonderdruckBandaufführung

167212

Environmental Pollution ; 158 (6), S. 2014-2022

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 PenmanşMonteith 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