The response of Norway spruce seedlings to simulated acid mist

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 of application 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 (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.