What was done
Seedlings of two rice cultivars were grown for 28 days in glasshouses receiving atmospheric CO2 concentrations of 373, 545, 723, and 895 ppm.  In addition, seedlings were fertilized with low, medium, or high levels of nitrogen to study the effects of elevated CO2 and soil nitrogen on rice productivity and growth.

What was learned
After four weeks of treatment, photosynthesis was found to significantly increase with increasing nitrogen availability and atmospheric CO2 concentration.  Averaged across all nitrogen regimes, for example, plants grown at 895 ppm CO2 exhibited photosynthetic rates that were about 50% greater than those observed in plants grown at ambient CO2.  Similarly, total plant dry weight also increased with soil nitrogen and atmospheric CO2.  The percentage enhancement resulting from CO2 enrichment, however, increased with soil nitrogen; from 21% at the lowest nitrogen concentration to 60% at the highest.

What it means
As the concentration of CO2 in the atmosphere continues to increase, rice plants will likely display higher rates of photosynthesis, regardless of nitrogen availability.  This phenomenon should enhance carbohydrate production in rice and allow plants to attain greater size, weight, and yield. And the greater the availability of nitrogen in the soil, the greater the anticipated growth increase.