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The paper concerns the potential effects of acidic deposition on the nutrient status of soil and forest and on the possible toxic effect of increased Al solubility. The nutrient status of trees may be influenced by pollutants interacting with the foliage and also by changing availability of nutrients in the soil. N compounds are often absorbed by the canopy whereas base cations are lost to the soil by foliar leaching. Cation leaching increases with increased acidity of precipitation. Throughfall acidity varies with tree species, season and distance from the emission areas. The impact of increased foliar leaching of base cations is not well known. In soil, acid deposition may have three effects: (i) a fertilizer effect caused by the deposition of N, and possibly, under specific conditions, also of S; (ii) an acidification effect caused by increased leaching of base cations; and (iii) an Al toxicity effect in cases where soil acidity is increased. Results of fertilizer experiments indicate that the atmospheric deposition of N is likely to increase forest growth especially in the northern parts of North America and Europe. At more southerly latitudes, nutrients in addition to N are often deficient. Therefore the N deposition is less likely to stimulate forest growth. Sulphur deposition is not likely to increase forest growth in most areas of the temperate zone. On the contrary, S deposition will mostly increase leaching of base cations such as Mg 2+ and Ca 2+ , and possibly K. Experiments with artificial acidification together with observations of increased Mg-deficiency in central Europe, indicate that Mg-deficiency might become a problem on sensitive soils exposed to acid deposition. The possibility of Al toxicity caused by increased soil acidity is discussed on the basis of experiments with seedlings of Norway spruce. It is concluded that Al toxicity appears to be unlikely unless the Al concentrations in the soil solution increase to about 20 mg l -1 .

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High inputs of N to N‐limited forests may disturb the nutrient balance of the plant‐soil system. The objective of this study was to quantify the effects of N and Mg applications on soil water chemistry in a 35‐ to 45‐yr‐old Scots pine (Pinus sylvestris L.) forest in southern Norway. Fertilizer applications began in 1990 and soil water sampling was carried out in May through October 1997 to 1999. Nine years with annual (one dose) inputs of 30 kg N ha−1 yr−1 increased the annual average nitrate N (NO3–N) leaching below the B horizon to ≈2.1 kg ha−1, compared with ≈0.1 kg ha−1 in the control plots. An input of 90 kg N ha−1 yr−1 resulted in symptoms of N saturation. The soil water concentration of NO−3 and ammonium (NH+4) increased, and the annual average leaching of inorganic N from May to October during the years 1997 to 1999 was ≈15 kg N ha−1 The N addition significantly reduced the concentrations of dissolved organic carbon and N (DOC and DON), but the contribution of DON to the total N leaching from the plots receiving the highest N dose was still large. Addition of 1.5 kg ha−1 yr−1 of Mg increased the DOC and DON concentrations. The reason for this is unknown, and further studies are needed to understand DOC and DON dynamics. Even though applications of high single N doses are not directly comparable to chronic N depositions of small doses in precipitation, the results indicate future consequences to pine forests growing under similar conditions.