Fig. 2.

Net fluxes (nmol m⁻² s⁻¹) of NH₄⁺ and NO₃⁻ at roots (the mature zone, 1·2 mm from the root tip) and fronds of Landoltia punctata exposed to different media (0·5, 1·0 or 2·5 mm NH₄NO₃). Values are means±s.e. (n=5). Different lower-case letters indicate significant differences (P≤0·05).