Carbon dioxide Concentration

Carbon dioxide is the major limiting factor for photosynthesis. The concentration of CO2 is very low in the atmosphere — between 0.03 and 0.04 per cent. An increase in concentration up to 0.05 per cent can cause an increase in CO2 fixation rates; beyond this, the levels can become damaging over longer periods.

C3 and C4 plants respond differently to CO2 concentrations:

• At low light conditions, neither group responds to high CO2.
• At high light intensities, both C3 and C4 plants show an increase in the rate of photosynthesis.
• C4 plants show saturation at about 360 microlitres per litre.
• C3 plants respond to increased CO2 concentration, and saturation is seen only beyond 450 microlitres per litre. …