Stomatal uptake of SO 2 , NO x and O 3 by spruce crowns ( Picea abies) and canopy damage in Central Europe

summary The stomatal uptake of SO 2 , NO 2 and O 3 by Norway spruce canopies ( Picea abies (L.) Karst.) has been integrated at six sites in central Germany (Königstein in the Taunus mountains. Witzenhausen, Grebenau, Frankenberg, Fürth in the Odenwald mountains and Biebergemünd in the Spessart mountains), Results are based on 788000 half‐hourly available sets of field data on air pollution and site meteorology measured since 1984 (45 site years). Data on stomatal water conductance are available from statistical response functions obtained in the field at all times of day and seasons of the year. From this, stomatal conductance was calculated fur different atmospheric tract gases. Statistical response functions are presented which allow the separate estimation of annual stomatal net uptake of trace gases in the field if only (i) measured annual means of SO 2 , NO 2 , and O 3 , pollution and (ii) the length of the trunk growth period (defined by temperature) are known. The following specific annual doses of stomatal trace‐gas net uptake in the field (μmol m −2 total needle surface d −1 annual trunk growth period/(nPa Pa −1 ) annual mean of trace gas concentration) are obtained; SO 2 : (0.157 ± 0.011) μmol m −2 d −1 /(nPa SO 2 , Pa −1 ), NO x : (0.4774 ± 0.034) μmol m −2 d −1 /(nPa NO 2 Pa −1 ), O 3 : (0.474 ± 0.034) μmol m −2 d −1 /(nPa O 3 Pa −1 ). There is an apparent NO 2 , compensation point at 7 nPa Pa −1 in the field if NO x (=NO 2 , + NO) fluxes are integrated; the individual NO 2 , compensation point equals c 3.2 nPa Pa −1 . Additionally, a statistical response function is presented, which estimates actual stomatal water transpiration rates in the field on the basis of measured water vapour pressure differences. VPD (mPa Pa −1 ). Complex canopy effects were calculated on the basis of available data using an effective leaf area which is 0×32 times the morphological leaf area index. Results are consistent (i) with available water balance data, (ii) with observed SO 2 ‐dependent sulphate accumulation rates in ...