Which factor will decrease photosynthesis

Light intensity and temperature are the two limiting factors that can decrease if present at extremely high levels.

Explanation:

The number of limiting factors that interact to make photosynthesis work such. The major factors are- carbon dioxide, temperature, and light intensity, however only light intensity decreases the photosynthesis process if present excessive high levels.  

Up to a certain level, light intensity tends to increase photosynthesis but after that level, it stops and if light intensity goes at an extremely high level it might decrease photosynthesis process.

At extremely high temperatures (above 104° F) the enzyme can be damaged and decrease the photosynthesis process.