Kinetics of ammonium and nitrate uptake among wild and cultivated tomatoes

Summary 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 NH₄⁺uptake differed among these taxa and were not dependent on the ionic composition of the nutrient solution. The kinetics of net NO₃^-uptake were dependent on the composition of the nutrient solution; the presence of NH₄⁺or Cl^- enhanced net NO₃^-uptake for the cultivated species and for a highland accession of the wild species. The capacity for net NO₃^-uptake was greater than the capacity for net NH₄⁺uptake in all three taxa; the proportion of NO₃^-to NH₄⁺absorbed was much greater for the wild taxa. Our data suggest that NO₃^-may be a more important source of mineral nitrogen than NH₄⁺for these tropical taxa.