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Keywords:

  • canopy structure;
  • free-air CO2 enrichment (FACE);
  • global change;
  • leaf area index;
  • model;
  • nitrogen;
  • photosynthesis;
  • rice (Oryza sativa)

Summary

  • • 
    Here we analysed the effects of CO2 (Ca) elevation and nitrogen availability on canopy structure, leaf area index (LAI) and canopy photosynthesis of rice (Oryza sativa).
  • • 
    Rice was grown at ambient and elevated Ca (c. 200 µmol mol−1 above ambient, using the free-air CO2 enrichment, FACE) and at two N availabilities. We measured leaf area, area-based leaf N contents and leaf photosynthesis, and calculated net daily canopy photosynthesis.
  • • 
    FACE plants had higher light-saturated rates of photosynthesis (Pmax) and apparent quantum yields than ambient plants, when measured at their own growth CO2. Ca elevation reduced the total leaf N in the canopy (Nleaf) but had no effect on LAI, and the average leaf N content (Nleaf/LAI) was therefore reduced by 8%. This reduction corresponded well with our model predictions. Leaf area index increased strongly with N availability, which was also consistent with our model.
  • • 
    Calculated canopy photosynthesis increased more strongly with Nleaf under elevated than under ambient Ca. This indicates that there is an N × Ca interactive effect on canopy carbon gain. This interaction was caused by the increase in LAI with N availability, which enhanced the positive effect of the higher quantum yield under Ca elevation.