The major limiting factor for photosynthesis is:

Carbon dioxide is the major limiting factor for photosynthesis. The concentration of ${\mathrm{CO}}_2$ is very low in the atmosphere (between 0.03 and 0.04 per cent). Increase in concentration upto 0.05 per cent can cause an increase in ${\mathrm{CO}}_2$ fixation rates; beyond this the levels can become damaging over longer periods.