According to Blackman's law of limiting factors, if a chemical process is affected by more than one factor, then the rate of reaction will be determined by the factor which is nearest to its minimal value.
Photosynthesis is affected by factors like light intensity, carbon dioxide concentration, temperature and water.
1. Light: if light increases, photosynthesis also increases upto a certain level. Then it remains constant. Plants need only 10% of the available light intensity of sunlight. Therefore, light is never a limiting factor except in case the plant is in shade or in dense forest.
If the light intensity increases too much, it starts destroying the chlorophyll, thus, photosynthesis reduces.
2. Carbon dioxide: if amount of carbon dioxide increases, photosynthesis also increases upto CO2 concentration of 0.05 %. Then photosynthesis reduces.
Saturation level or optimum level of carbon dioxide for C4 plants is 360 microlitre per litre of air; and for C3 plants is 450 microlitre per litre of air. Thus, carbon dioxide is a limiting factor more for C3 plants.
3. Temperature: if temperature increases, photosynthesis also increases upto a certain level. Then photosynthesis reduces. C3 plants have lower optimum temperature (18 to 24 degree celsius). C4 plants have a little higher optimum temperature (30 to 40 degree celsius).
4. Water: if available water is more, photosynthesis increases up to a certain level. Then there is no effect. If water available is less, the stomata do not open fully. So absorption of carbon dioxide is less. Thus, photosynthesis will also be less.
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