Meaning and mechanism
Photosynthesis is the process of converting light energy into the fixation of carbon into organic matter. Factors such as light, the supply of carbon dioxide, and the temperature at which enzymes function, all have an influence.
In dim light, the effect of increased illumination is significant, but in sufficient light, it can be limited by processes such as carbon dioxide or other factors. The limiting factors change depending on the conditions.
Relationships and conditions
The experiment is a model where the smaller of light limitation and CO₂ limitation is combined with the temperature coefficient. When comparing the effect of one variable, the remaining conditions are kept constant.
Actual photosynthesis also depends on water status, stomata, nutrients, photoinhibition, and plant species. Gross photosynthesis must also be distinguished from net production after respiration is subtracted.
What to observe in the simulation
Light and CO₂ are each saturated. The speed can only be increased by increasing the insufficient supply. The temperature coefficient is largest around 30 °C.
This is a virtual model of Hydrilla. Light intensity and sodium bicarbonate concentration feed relative light and CO₂-supply functions; they are not converted to actual dissolved CO₂ concentrations. The model uses light/(30+light), supply/(0.3+supply), and exp(−((T−30)/12)²). Each bubble represents the same simulated oxygen amount. Respiration, bubble size, gas dissolution, biomass, and species-specific optimum temperatures are omitted.
Key relationships and symbols
Speed = min (light limitation, CO₂ limitation) × temperature coefficient × 3
| Symbol | Meaning | Unit |
|---|---|---|
| CO₂ | Carbon dioxide supplied for photosynthesis | Concentration |
| Limiting factor | The current speed is the condition that most strongly restricts it. | Units depend on the conditions |
Worked example
Why is the speed from luminosity 40 → 100 the same at low CO₂?
Use the smaller of the light limit and CO₂ limit. If the light intensity is already sufficient at low CO₂, increasing the CO₂ will increase the speed.
Common misconceptions
- Increasing the light by two-fold does not result in double the photosynthesis under all conditions.