Tundra plant uptake of amino acid and NH4+ nitrogen in situ: Plants compete well for amino acid N

Traditional models of nutrient cycling assume that soil microorganisms must decompose organic matter, releasing inorganic N, to make N available to plants. Several lines of evidence have raised doubts about this assumption In arctic tundra, but no firm evidence existed. Here we demonstrate that Eriophorum vaginatum and Carer aquatilis, two tundra sedges, compete well for glycine and aspartate N relative to NH4+ in situ. At relatively high concentrations (25 mu g N/g soil), during the peak 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 mechanism of amino acid mineralization followed by plant uptake of the released N. These results indicate that these tundra plants have active mechanisms for enhancing their access to amino acid N in situ.