The study looked at how different levels of CO2 affected the growth and photosynthesis of rice and winter wheat. They found that higher CO2 levels decreased the net photosynthetic rate and leaf nitrogen content in rice, but increased the rate of photosynthesis. This led to more biomass and yield in both crops. Lower CO2 levels had little effect on the plants. Overall, higher CO2 levels had a bigger impact on the growth and photosynthesis of these plants compared to lower CO2 levels.