Modelling of stomatal conductance and ozone flux of Norway spruce: comparison with field data

It has been proposed that stomatal flux of ozone would provide a more relia ble basis than ozone exposure indices for the assessment of the risk of ozo ne damage to vegetation across Europe. However, implementation of this appr oach requires the development of appropriate models which need to be rigoro usly tested against actual data collected under field conditions. This pape r describes such an assessment of the stomatal component of the model descr ibed by Emberson et al. (2000. Modelling stomatal ozone flux across Europe. Environmental Pollution 110). Model predictions are compared with field me asurements of both stomatal conductance (g(s)) and calculated ozone flux fo r shoots of mature Norway spruce (Picea abies) growing in the Tyrol Mountai ns in Austria. The model has been developed to calculate g(s) as a function of leaf phenology and four environmental variables: photosynthetic Aux den sity (PFD), temperature, vapour pressure deficit (VPD) and soil moisture de ficit (SMD). The model was run using climate data measured on site, althoug h the SMD component was omitted since the necessary data were not available . The model parameterisation for Norway spruce had previously been collecte d from the scientific literature and therefore established independently fr om the measurement study. Overall, strong associations were found between m odel predictions and measured values of stomatal conductance to ozone (GO(3 )) and calculated stomatal ozone flux (FO3). Average diurnal profiles of GO (3) and FO3 showed good agreement between the field data and modelled value s except during the morning period of 1990. The diurnal pattern of ozone fl ux was determined primarily by PFD and VPD, as there was little diurnal var iation in ozone concentration. In general, the model predicted instances of high ozone flux satisfactorily, indicating its potential applicability in identifying areas of high ozone risk for this species. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.