Identifying limits on photosynthesis

Photosynthesis depends on interacting factors including light, carbon dioxide supply, and temperature. Increasing one factor may improve the rate only until another factor becomes limiting. A plateau does not mean the process has stopped. Suppose increasing light raises the rate at first, but the rate then levels off. If adding carbon dioxide at that point raises the rate further, carbon dioxide availability was limiting under those conditions. Controlled changes help distinguish possible explanations.