At six sites in central Germany consequences of SO2, NOx and O-3 depos
ition and of acid precipitation on canopy throughfall of sulphate, nit
rate, ammonium, organic acids and of metal cations from Norway spruce
crowns were investigated in the field. Measured canopy throughfall rat
es (mmol ion kg(-1) needle dw a(-1) are separated in (i) ''background'
' ion throughfall rates in clean air and (ii) trace gas- (or acid inte
rception)-dependent throughfall rates at ambient trace gas concentrati
ons. Based on synchronously measured pollution, precipitation and cano
py throughfall data, statistical response functions are given, which a
llow the separate estimation of annual rates of sulphur and nitrogen d
eposition into spruce canopies if only annual means of SO2 or NO2 conc
entrations in air are known. The specific SO2 deposition rate of (0.84
1+/-0.214) mmol S kg(-1) needle dw a(-1) (nPa SO2 Pa-1)(-1) is 2.3 tim
es higher than the specific stomatal SO2 uptake. The NO2-dependent nit
rogen deposition of (2.464+/-0.707) mmol N kg(-1) needle dw a(-1) (nPa
NO2 Pa-1)(-1) is 2.2 times higher than the specific stomatal NOx (NO2
+ NO) uptake. These ratios (2.3 approximate to 2.2) are explained by
the percentage of annual hours with open needle stomata. The shape of
observed ''epicuticular'' SO2 and NOx deposition curves and of stomata
l SO2 and NOx uptake curves are congruent. As for stomatal NOx uptake,
there is an apparent compensation point at (5 to 8) nPa NO2 Pa-1. The
re is significant SO2-dependent canopy throughfall of Ca>K>Al>Mg>Fe in
this order of relative importance. NOx deposition in spruce canopies
reduces K+ throughfall and it weakly promotes throughfall of Mn2+ and
Zn2+. There was no significant codeposition of sulphate and ammonium a
nd no ion exchange of intercepted H3O+ with nutrient cations at the me
asured ambient pH values of the precipitation water. In the presence o
f O-3, throughfall of Mn2+ is reduced and throughfall of K+, Ca2+ and
Al3+ is enhanced. In the cooperative presence of SO2, NO2 and O-3 poll
ution in the field there is a 1.3-fold increase of the annual K+ deman
d and a 1.5-fold Mg2+ demand of spruce canopies relative to the situat
ion in clean air. This trace gas-dependent additional cation demand of
spruce canopies corresponds to a needle loss percentage of (23 to 33)
% if the additional K+ and Mg2+ throughfall could not be recycled in s
pruce ecosystems. Observed canopy thinning ranges from (13 to 26)% at
the investigated six spruce stands.