Compartmentation and flux characteristics of ammonium in spruce

Abstract

Using 13NH4+as a tracer, compartmental analyses for NH4+were performed in non-mycorrhizal roots of intact Picea glauca (Moench) Voss. seedlings at four different concentration regimes of external NH4+([NH4+]o), i.e. 0, 10, 100, and 1500 μM. Three kinetically distinct compartments were identified, with half-lives of exchange of approximately 2 s, 30 s, and 14 min, assumed to represent surface adsorption, Donnan free space, and cytoplasm, respectively. No significant differences were found in half-lives of exchange with changes in [NH4+]o. Influx was calculated to be 0.96 μmol·g−1·h−1 in N-deprived plants (measured at 10 μM [NH4+]o), while under steady-state conditions it was 0.21 μmol·g−1h−1 ..