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). 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.