Factors affecting the rate of photosynthesis
Water
You won't often 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.
The rate of photosynthesis will also change during the year in countries like the UK.
Carbon dioxide
Levels of carbon dioxide in the atmosphere are rising because of The gases responsible for global warming - carbon dioxide, methane, nitrous oxide and CFCs (chlorofluorocarbons). 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:
| Crop | Optimum temperature in °C | Maximum temperature in °C | Minimum temperature in °C |
| Maize | 22–25 | 34 | 20 |
| Potato | 15–20 | 34 | 12 |
| Rice | 30–33 | 40 | 18 |
| Soya beans | 25–28 | 40 | 10 |
| Wheat | 20–25 | 38 | 5 |
| Crop | Maize |
|---|---|
| Optimum temperature in °C | 22–25 |
| Maximum temperature in °C | 34 |
| Minimum temperature in °C | 20 |
| Crop | Potato |
|---|---|
| Optimum temperature in °C | 15–20 |
| Maximum temperature in °C | 34 |
| Minimum temperature in °C | 12 |
| Crop | Rice |
|---|---|
| Optimum temperature in °C | 30–33 |
| Maximum temperature in °C | 40 |
| Minimum temperature in °C | 18 |
| Crop | Soya beans |
|---|---|
| Optimum temperature in °C | 25–28 |
| Maximum temperature in °C | 40 |
| Minimum temperature in °C | 10 |
| Crop | Wheat |
|---|---|
| Optimum temperature in °C | 20–25 |
| Maximum temperature in °C | 38 |
| Minimum temperature in °C | 5 |
Most scientists think that with rising temperatures, crop production will be negatively affected by climate change.
Chlorophyll
Plants grown in shady places increase the chlorophyll content of their leaves so that they can absorb the necessary light energy required for photosynthesis.
The compensation point is where light intensity is at the point where the rate of photosynthesis is equal to the rate of respiration. At light intensities below this point, more respiration occurs. At higher light intensities, more photosynthesis occurs. The position of the compensation point is different from plants grown in brighter conditions.
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.