Limiting factors for Photosynthesis

For photosynthesis to occur, the following are required:

1. photosynthetic pigments (e.g. chlorophyll) - these absorb light energy

2. carbon dioxide - this provides carbon to make glucose

3. water - this provides electrons and is a source of hydrogen ions (protons)

4. light - this provides energy to split water, to provide ATP, and to reduce NADP

5. a suitable temperature - this provides kinetic energy for reactions

A limiting factor is a requirement that is in shortest supply. Increasing this factor allows the rate of photosynthesis to increase. Main factors limiting the rate of photosynthesis are:

1. light intensity

2. carbon dioxide concentration

3. temperature

Low light intensity

This limits the light dependent stage, so not much ATP and reduced NADP are produced. This slows the light-independent stage, and the rate of photosynthesis is low

Intermediate light intensity

This produces more ATP and reduced NADP in the light dependent stage, which regenerates RuBP in the light-independent stage more quickly. More GP gets converted to triose phosphate, and the rate of photosynthesis increases

Very high light intensity

There is more light than needed, so another factor like temperature becomes limiting and the rate plateaus

The light compensation point

When the volume of oxygen is produced and carbon dioxide absorbed in photosynthesis is balanced by the oxygen absorbed and the carbon dioxide produced by respiration

Low carbon dioxide concentration

This limits the light-independent reaction as less carbon dioxide is fixed, reducing the production of GP and triose phosphate. The rate of photosynthesis is low

Intermediate carbon dioxide concentration

this allows faster production of GP and triose phosphate increasing the rate of photosynthesis

High carbon dioxide concentration

another factor like light becomes limiting

Saturation point

When the factor being measured is no longer limiting the reaction and something else is the limiting factor

Low temperature

this provides little kinetic energy, slowing the enzyme catalysed stages of photosynthesis, like the fixation of carbon dioxide controlled by rubisco. The rate of photosynthesis is low

Intermediate temperature

this increases the kinetic energy supplied to these reactions, increasing the rate of photosynthesis up to an optimum point

Very high temperature

this denatures enzymes, so the rate of photosynthesis drops sharply