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 (N leaf) 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 x C a 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.
- Canopy structure
- Free-air CO enrichment (FACE)
- Global change
- Leaf area index
- Rice (Oryza sativa)