Performance of two Picea abies ( L . ) Karst . at different stages of decline VI . Nutrient concentration stands

A declining Picea abies (L.) Karst. stand produced as much foliage and branches as a healthy stand but less stemwood at a similar leaf area index and climate. Nutrient analyses revealed that most biomass components at the declining site had lower concentrations of calcium and magnesium, but similar nitrogen and potassium (except for lower potassium in younger needles) and higher phosphorus , manganese and aluminum than the respective components at the healthy site. Comparison of these data with the results from studies on the nutrition and growth of P. abies seedlings (Ingestad 1959) led to the conclusion that the healthy stand is in a balanced nutritional state, while trees at the declining stand have only 56% of the foliar magnesium concentration required to permit growth at a rate which could be achieved at their nitrogen status. It appears that acidic deposition, which involves an input of nitrogen and a leaching of cations from the soil, causes an imbalance in the availability of nitrogen and magnesium. Growth is eventually reduced as magnesium becomes limiting. The impact of sulfate and nitrate in acidic deposition on the flutritional status of forests may be positive or negative. Initially, a positive effect on growth from increased nitrogen and sulfur availability nutrition may dominate if cation capital in the soil is ample but nitrogen is limiting growth (Nihlgfird 1985; Schulze et al. 1987; Tamm and Aronsson 1988). Then, a nutritional imbalance may develop when acidic deposition accelerate cation leaching from soils (Ul-rich 1986) while tree growth is still promoted by an elevated nitrogen supply (Nihlggtrd 1985; Schulze et al. 1987). Eventually , decline in tree vigor and forest productivity is expected as nutritional deficiencies develop to a level which impair physiological processes. Therefore, when cation supply from the soil barely meets stand demands, acidic deposi-tion is likely to cause a short term increase in growth, followed by a continuous decline in productivity (Tamm and Aronsson 1988). A reduction in stand productivity may result from reduced production per unit of leaf area, from loss of canopy leaf area, or both. Reduction in production rate and in leaf area may result from nutritional and non-nutritional (i.e. direct damage to needles) effects of air pollution (John-son et al. 1982). Non-nutritional effects would most likely be the major cause of decline in areas where SO2, NOx and 03 levels are high (Amundson et al. 1986, see also review by Kozlowski …