Kinetics of ammonium and nitrate uptake among wild and cultivated tomatoes.

Concentration dependence of net ammonium and nitrate uptake was monitored for a cultivar of tomato, Lycopersicon esculentum, and two accessions of a neotropical wild relative, L. hirsutum. The kinetics of net NH 4+ uptake differed among these taxa and were not dependent on the ionic composition of the nutrient solution. The kinetics of net NO 3- uptake were dependent on the composition of the nutrient solution; the presence of NH 4+ or Cl- enhanced net NO 3- uptake for the cultivated species and for a highland accession of the wild species. The capacity for net NO 3- uptake was greater than the capacity for net NH 4+ uptake in all three taxa; the proportion of NO 3- to NH 4+ absorbed was much greater for the wild taxa. Our data suggest that NO 3- may be a more important source of mineral nitrogen than NH 4+ for these tropical taxa.