STOMATAL UPTAKE OF SO2, NOX AND O-3 BY SPRUCE CROWNS (PICEA-ABIES) AND CANOPY DAMAGE IN CENTRAL-EUROPE

The stomatal uptake of SO2, NOx and O-3 by Norway spruce canopies (Pic ea abies (L.) Karst.) has been integrated at six sites in central Germ any (Konigstein in the Taunus mountains, Witzenhausen, Grebenau, Frank enberg, Furth in the Odenwald mountains and Biebergemund in the Spessa rt mountains). Results are based on 788 000 half-hourly available sets of held data on air pollution and site meteorology measured since 198 4 (45 site years). Data on stomatal water conductance are available fr om statistical response functions obtained in the field at all times o f day and seasons of the year. From this, stomatal conductance was cal culated for different atmospheric trace gases. Statistical response fu nctions are presented which allow the separate estimation of annual st omatal net uptake of trace gases in the field if only (i) measured ann ual means of SO2, NO2 and O-3 pollution and (ii) the length of the tru nk growth period (defined by temperature) are known. The following spe cific annual doses of stomatal trace-gas net uptake in the field (mu m ol m(-2) total needle surface d(-1) annual trunk growth period/(nPa Pa -1) annual mean of trace gas concentration) are obtained; SO2: (0.157 +/- 0.011) mu mol m(-2) d(-1)/(nPa SO2 Pa-1), NOx: (0.477 +/- 0.035) m u mol m(-2) d(-1)/(nPa NO2 Pa-1), O-3: (0.474 +/- 0.034) mu mol m(-2) d(-1)/(nPa O-3 Pa-1). There is an apparent NO2 compensation point at 7 nPa Pa-1 in the field if NOx (= NO2 + NO) fluxes are integrated; the individual NO2 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 measur ed water vapour pressure differences, VPD (mPa Pa-1). Complex canopy e ffects were calculated on the basis of available data using an effecti ve leaf area which is 0.32 times the morphological leaf area index. Re sults are consistent (i) with available water balance data, (ii) with observed SO2-dependent sulphate accumulation rates in spruce needles a nd (iii) with observed epicuticular SO2 deposition rates. Pollution da ta are compared with observed damage of spruce canopies in the field. There was a statistically significant correlation between observed dam age to spruce canopies and ambient SO2 concentrations in air. No such correlation could be observed between spruce decline and concentration s of NO2 and O-3. Physiological consequences of chronic trace gas upta ke are discussed.