Four pot experiments are reported in which Norway spruce (Picea abies
(L.) Karst) seedlings, of different nutrient status, were treated with
acid mist for one growing season in open-top chambers (OTCs). Combina
tions of H+, SO42-, NH4+ and NO3- were applied at different frequencie
s of application and supplying different doses of S and N kg ha-1. Pla
nt growth, visible injury, frost hardiness and nutrient status were ob
served. These experiments were undertaken to improve our understanding
of the interaction of environmental factors such as nutrition and mis
t-exposure frequency on seedling response to N and S deposition.Both a
cidity (less than or equal to pH 2.7) and SO42- ions were necessary to
induce visible injury. Mist containing SO42-,2-, Hi and to a lesser e
xtent NH4+ significantly reduced winter frost hardiness. Increasing th
e misting frequency, and to a lesser extent the overall dose, increase
d the likelihood of acid mist causing visible injury and reducing fros
t hardiness. Post-planting stress, low N status and needle juvenility
increased the likelihood of acid mist causing visible injury. Increase
d plant vitality, adequate N status and growth rate reduced the likeli
hood of acid-mist-induced reductions in frost hardiness. Principles un
derlying the responses of spruce seedlings treated in controlled condi
tions to acid mist are discussed.