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). Combinations of H+,
SO42−, NH4+ and
NO3− were applied at different frequencies
and supplying different doses of S and N kg ha−1.
Plant growth, visible injury, frost hardiness and nutrient status were
observed. These experiments were
undertaken to improve our understanding of the interaction of
environmental factors such as nutrition and mist-exposure frequency on
seedling response to N and S deposition.
Both acidity ([les ]pH 2·7) and SO42−
ions were necessary to induce visible injury. Mist containing
SO42−, H+ and to a lesser extent
NH4+ significantly reduced winter frost hardiness.
Increasing the misting frequency, and to a
lesser extent the overall dose, increased the likelihood of acid mist
causing visible injury and reducing frost
hardiness. Post-planting stress, low N status and needle juvenility
increased the likelihood of acid mist causing
visible injury. Increased plant vitality, adequate N status and growth
rate reduced the likelihood of acid-mist-induced reductions in frost hardiness.
Principles underlying the responses of spruce seedlings treated in
controlled conditions to acid mist are discussed.