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Keywords:

  • Jmax;
  • limiting step;
  • mesophyll conductance (gm);
  • nitrogen;
  • photosynthesis;
  • RuBP carboxylation;
  • RuBP regeneration;
  • stomatal conductance (gs);
  • Vcmax

ABSTRACT

Effects of nitrogen (N) supply on the limiting step of CO2 assimilation rate (A) at 380 µmol mol−1 CO2 concentration (A380) at several leaf temperatures were studied in several crops, since N nutrition alters N allocation between photosynthetic components. Contents of leaf N, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) and cytochrome f (cyt f) increased with increasing N supply, but the cyt f/Rubisco ratio decreased. Large leaf N content was linked to a high stomatal (gs) and mesophyll conductance (gm), but resulted in a lower intercellular (Ci) and chloroplast CO2 concentration (Cc) because the increase in gs and gm was insufficient to compensate for change in A380. The A-Cc response was used to estimate the maximum rate of RuBP carboxylation (Vcmax) and chloroplast electron transport (Jmax). The Jmax/Vcmax ratio decreased with reductions in leaf N content, which was consistent with the results of the cyt f/Rubisco ratio. Analysis using the C3 photosynthesis model indicated that A380 tended to be limited by RuBP carboxylation in plants grown at low N concentration, whereas it was limited by RuBP regeneration in plants grown at high N concentration. We conclude that the limiting step of A380 depends on leaf N content and is mainly determined by N partitioning between Rubisco and electron transport components.