Does nitrogen concentration affect relative uptake rates of nitrate, ammonium, and glycine?

Weinheim

2009

S. 224-229

3 Abb., 1 Tab., 42 Lit. Ang.

Artikel aus einer ZeitschriftUnselbständiges Werk

200155345

Plant roots are exposed to a variety of nitrogen forms (e.g., nitrate, ammonium, amino acids) and take up these forms at different rates. Many studies have investigated whether plants prefer nitrate, ammonium, or amino acids; but studies may not be comparable because they used substrate concentrations between 100 and 2000 mol L-1. This study tests the hypothesis that substrate concentrations from 10 to 1750 mol L-1 affect plant preference for N forms. Nitrogen uptake by the herb Ocimum basilicum and the evergreen tree Eucalyptus regnans was examined by placing roots of intact seedlings in equimolar mixtures of nitrate, ammonium, and glycine in which one of the N forms was 15N-labelled (and 13C-labelled in the case of glycine). In both species, preference for N forms was affected by substrate concentration. At 10 mol L-1 (O. basilicum) or 10 and 50 mol L-1 (E. regnans), rates of N uptake did not differ among N forms. At substrate concentrations of 50 mol L-1 and greater O. basilicum took up ammonium the fastest, glycine the slowest, and nitrate at an intermediate rate. At substrate concentrations from 100 to 1750 mol L-1, E. regnans took up ammonium the fastest with glycine and nitrate taken up at slower rates. The absence of significant differences at lower concentrations was a true biological effect rather than a function of larger relative errors. This study demonstrates that substrate concentration has a large effect on plant preference for N forms, and sounds a warning for studies of N nutrition that do not consider the concentration-dependence of plant preference for N forms.