Table 5.

Differences between ammonium (${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$), nitrate (${\mathrm{N}\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$), glutamine-N (Gln-N), and arginine-N (Arg-N) net uptake capacity of the fine roots of Prunus serotina and Robinia pseudoacacia seedlings grown single and in competition at low and high soil N availability.

	Soil N availability	Prunus	Robinia
Single grown seedlings	Low	n.s.	Gln-N, Arg-N > ${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$
	High	${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$, Arg-N > Gln-N > ${\mathrm{N}\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$	n.s.
Seedlings in competition with Fagus	Low	n.s.	n.s.
	High	${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$, Arg-N > Gln-N, ${\mathrm{N}\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$	${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$, Gln-N, Arg-N > ${\mathrm{N}\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$
Seedlings in competition with Quercus	Low	Arg-N > ${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$, ${\mathrm{N}\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$	Gln-N, Arg-N > ${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$
	High	${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$, Arg-N > ${\mathrm{N}\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$, Gln-N	n.s.
Seedlings in competition with Pinus	Low	Arg-N > ${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$, Gln-N	Gln-N, Arg-N > ${\mathrm{N}\mathrm{H}}_{\mathrm{4}}^{\mathrm{+}}$, ${\mathrm{N}\mathrm{O}}_{\mathrm{3}}^{\mathrm{-}}$
	High	n.s.	n.s.

Only significant differences are presented. n.s., no significant differences between net uptake capacity of different N forms.