ACCUMULATION OF AMINO-ACIDS IN SOME BOREAL FOREST PLANTS IN RESPONSE TO INCREASED NITROGEN AVAILABILITY

Accumulation of amino acids in response to application of 500 kg N ha(-1) as a single dose of NH4NO3 was measured for four common Swedish forest species. Addition of N resulted in increased levels of especially glutamine and arginine in Vaccinium myrtillus L. and in V. vitis-idaea L., whilst, in fertilized Deschampsia flexuosa L., asparagine and glutamine were most prominent. In Epilobium angustifolium L. glutamine and arginine increased most after fertilization. In a second study, five different forest species, V. myrtillus, V. vitis-idaea, D. flexuosa, Pleurozium schreberi Wild. and Polytrichum commune Menz. were studied in a Norway spruce fertilization experiment. In this experiment, plots had been irrigated with a complete mixture of nutrients during the growing period for five subsequent years. Arginine in Pl. schreberi, glutamine in P. commune and asparagine in D. flexuosa were all elevated on fertilized plots, while in fertilized V. vitis-idaea and V. myrtillus only minor increases of amino acid concentrations were found. In a third investigation, amino acid concentrations were measured in Pl. schreberi, Hylocomium splendens L., V. myrtillus, V. vitis-idaea and D. flexuosa growing on different plots in an area with relatively high nitrogen deposition. The plots were divided into two groups, one characterized by high, and one by low concentration of arginine in spruce needles from trees growing on the same plot. Asparagine in D. flexuosa, arginine and asparagine in Pl. schreberi and arginine in H. splendens were significantly higher in plants from plots with high concentrations of arginine in needles of Norway spruce. Differences between species in the metabolism of nitrogen during conditions of high nitrogen supply are discussed as well as possible usage of specific amino acids in the studied species as indicators of nitrogen saturation.