#44 Limiting factors in photosynthesis

Limiting factor is something present in the environment in such short supply that it restricts life processes.  Three factors can limit the speed of photosynthesis - light intensity, carbon dioxide concentration and temperature.

If a component is in low supply then productivity is prevented from reaching maximum.

Sunlight 

• Light energy is vital to the process of photosynthesis. It is severely limiting at times of partial light conditions, e.g. dawn or dusk.
• As light intensity increases, the rate of photosynthesis will increase, until the plant is photosynthesising as fast as it can. At this point, even if light becomes brighter, the plant cannot photosynthesise any faster.

• Over the first part of the curve (between A and B), light is a limiting factor. The plant is limited in how fast it can photosynthesise because it does not have enough light.
• Between B and C, light is not a limiting factor. Even if more light is shone on the plant, it still cannot photosynthesise any faster.

Carbon dioxide

• In photosynthesis CO₂ is a key limiting factor. The usual atmospheric level of CO₂ is 0.03%. In perfect conditions of water availability, light and temperature this low CO₂ level holds back the photosynthetic potential.
• The more CO₂ a plant is given, the faster it can photosynthesise up to a point, but then a maximum is reach. 

Temperature

The chemical reactions of photsynthesis can only take place very slowly at low temperature, so a plant can photosynthesise faster on a warm day than on a cold one.