What factors affecting photosynthesis?

The various factors that affect rate of photosynthesis are:
  • Light

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

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

    • Dark reactions are more sensitive to an increase in temperature.
    • 4  plants respond more to an increase in temperature as compared to C 3  plants.
    • Adaptations according to habitat also effect temperature optima. Tropical plants have higher temperature optima compared to temperate.
  • Water

    • Water stress causes stomata to close and hence, less CO 2  is available.
    • Water stress causes the leaves to wilt, thereby reducing their surface area and metabolic activity as well.

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