TUNDRA PLANT UPTAKE OF AMINO-ACID AND NH4-SITU - PLANTS COMPETE WELL FOR AMINO-ACID N( NITROGEN IN)

Traditional models of nutrient cycling assume that soil microorganisms must decompose organic matter, releasing inorganic N, to make N avail able to plants. Several lines of evidence have raised doubts about thi s assumption In arctic tundra, but no firm evidence existed. Here we d emonstrate that Eriophorum vaginatum and Carer aquatilis, two tundra s edges, compete well for glycine and aspartate N relative to NH4+ in si tu. At relatively high concentrations (25 mu g N/g soil), during the p eak of the season, E. vaginatum took up amino acid N more rapidly than NH4+ while later in the season and at lower concentrations (2-4 mu g N/g soil) both E. vaginatum and C. aquatilis took up glycine N and NH4 + at similar rates. These results are incompatible with a simple mecha nism of amino acid mineralization followed by plant uptake of the rele ased N. These results indicate that these tundra plants have active me chanisms for enhancing their access to amino acid N in situ.