ACCUMULATION OF AMINO-ACIDS IN FOREST PLANTS IN RELATION TO ECOLOGICAL AMPLITUDE AND NITROGEN SUPPLY

1. Field experiments were conducted to examine how total nitrogen (N) concentration and accumulation of free amino acids in boreal forest plants were affected by nitrogen supply. Nine species, including grasses, herbs and one ericaceous dwarf shrub, were fertilized with ammonium and nitrate (30 g N m(-2)), respectively. Leaves, rhizomes and roots were harvested 10 and 65 days after fertilization. The experiments were done in two spruce-dominated forest ecosystems that differed in biodiversity and productivity. 2. With some exceptions, ammonium fertilization gave the largest increase in both total N concentration and amino acid accumulation. The increase in total N was largely caused by an increase in amino acid N. 3. Glutamine N showed the largest response to fertilization and dominated the amino acid N pool 10 days after fertilization. Fertilization gave a more significant effect in the less productive forest. 4. At the end of the growing season, 65 days after fertilization, species typical of nutrient-rich habitats (Filipendula ulmaria, Lactuca alpina and Poa remota), had mainly accumulated asparagine, while species typical of poorer habitats (Geranium sylvaticum, Maianthemum bifolium and Vaccinium myrtillus), had accumulated arginine in rhizomes and roots as a response to increased N availability.