Elevated CO2 and nitrogen availability have interactive effects on canopy carbon gain in rice
2004
Anten, N. P. R. | Hirose, T. | Onoda, Y. | Kinugasa, T. | Kim, H. Y. | Okada, M. | Kobayashi, K.
• 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.
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