Affecting photosynthesis

Water

In the UK, water is often the main limiting factor for photosynthesis.

You won't see graphs for its effects, as water is important in many other areas of a plant's life, and not just photosynthesis. Most important is its role as a solvent for all the chemical reactions in cells.

Light

Light intensity affects the rate of photosynthesis. The light intensity fluctuates during the day, and will also be affected by the weather. The rate of photosynthesis will change with the time of day.

A graph showing the rate of photosynthesis.

The rate of photosynthesis will also change during the year in countries like the UK.

A graph showing the net production.

Carbon dioxide

Levels of carbon dioxide in the atmosphere are rising because of greenhouse gas emissions. They are currently at around 0.04 per cent. This concentration is still very low in terms of being the optimum for photosynthesis.

Carbon dioxide concentration is therefore an important limiting factor for photosynthesis.

Temperature

Plants can photosynthesise over a wide range of temperatures from 0°C to around 50°C.

The optimum temperature for most plants is 15°C to around 40°C.

Temperature affects the rate of photosynthesis in crop plants and affects where certain crops can be grown.

The table is an example of the optimum and maximum temperatures for the growth of some crops:

CropOptimumMaximumMinimum
Maize22 - 25°C34°C20°C
Potato15 - 20°C34°C12°C
Rice30 - 33°C40°C18°C
Soya beans25 - 28°C40°C10°C
Wheat20 - 25°C38°C5°C

Most scientists think that with rising temperatures, crop production will be negatively affected by climate change.

Chlorophyll

The position of the compensation point is different from plants grown in brighter conditions.

A graph showing the uptake of carbon dioxide and arbitrary units.

For shade-adapted plants, the compensation point is lower – their rate of photosynthesis will exceed the rate of respiration at lower light intensities than the plants adapted to sun.