Nitrogen deposition in Swiss forests and its possible relevance for leaf nutrient status, parasite attacks and soil acidification

Throughfall measurements in adult stands of Norway spruce across Switzerland below 1500 m a.s.l. revealed N loads of 18–33 kg N ha−1 year−1 and in alpine stands> 1500m a.s.l. 6–11 kg N ha−1 year−1. In permanent observation plots beech showed increasing foliar N concentrations between 1984 and 1995. At the same time, P concentrations decreased in both beech and Norway spruce, leading to increased N/P ratios. Foliar N concentrations of Norway spruce were significantly correlated with modelled N deposition. A rising Mn concentration in beech leaves between 1984 and 1995 suggests soil acidification during that period. N fertilization experiments with potted young beech and Norway spruce revealed similar nutrient shifts than those observed in the forest. In addition, increasing shoot-root ratio, soil acidification and increased susceptibility to parasite attacks were found with increasing N fertilization.