What abiotic factors affect photosynthesis?

Photosynthesis:

1. It is the process by which green plants use light energy to synthesize carbon dioxide and water.
2. The various factors which affect the rate of photosynthesis are:

1. Light:

1. Incident light is directly proportional to CO₂ fixation rate; but at the higher light intensities, its rate does not increase further as other factors become limiting.
2. Light is also rarely a limiting factor (with the exception of shade plants or plants of the dense forest) as light saturation occurs at 10% of the full sunlight.
3. Beyond a point, if the incident light is increased, it leads to a decrease in photosynthesis due to the breakdown of chlorophyll.

2. CO₂ Concentration:

1. Major limiting factor.
2. Usually low in the atmosphere (0.03 − 0.04%), Up to 0.05% − increases rate of CO₂ fixation, > 0.05% − damaging effect.
3. Though both the C₃ and C₄ show an increase in the rate of photosynthesis at high light intensity accompanied by high CO₂ concentration.
4. This saturation point for the C₃ is obtained at higher concentrations as compared to the C₄.
5. Therefore, CO₂ concentration is more of a limiting factor for C₃ plants.
6. Increased CO₂ concentration is also beneficial for greenhouse crops such as tomatoes and bell paper.

3. Temperature:

1. Dark reactions are more sensitive to increases in temperature.
2. C₄ plants respond more to an increase in temperature as compared to C₃ plants.
3. Adaptations according to a habitat also affect the temperature optima. Tropical plants generally have higher temperatures compared to temperate ones.

4. Water:

1. Water stress causes stomata to close and hence, less CO₂ is also available.
2. Water stress causes leaves to wilt, thereby reducing the surface area & metabolic activity as well.