NITROGEN STORAGE FORMS IN 9 BOREAL UNDERSTOREY PLANT-SPECIES

Storage forms of N were studied in belowground structures of nine bore al forest understorey plants. The ericaceous shrubs Vaccinium vitis-id aea and V. myrtillus, the fern Gymnocarpium dryopteris, the grass Desc hampsia flexuosa, and the herbs Epilobium angustifolium, Maianthemum b ifolium, Solidago virgaurea, Geranium sylvaticum and Trientalis europa ea were sampled in early summer and late autumn from plots fertilised with a complete mixture of nutrients and from non-fertilised control p lots. Concentrations of total nitrogen, insoluble and soluble proteins , free amino acids and nitrate were measured, and changes in absolute and relative concentrations of these N fractions between early summer and late autumn were used to identify the forms in which the plants st ore N. In all species studied, the concentration of free amino acids i ncreased both between summer and autumn and in response to fertilisati on, while the concentration of protein N increased only in response to fertilisation. Thus, free amino acids appear to have a central role i n N storage. In all of the species except G. dryopteris, D. flexuosa a nd S. virgaurea, arginine dominated the pool of free amino acids and t hus arginine was the major form of stored N in most species. In D. fle xuosa and S. virgurea, however, asparagine and arginine together were the major forms of stored N, while glutamine was the major free amino acid, and N storage form, in G. dryopteris.