Below are the limiting factors of Photosynthesis:
- Light Intensity
- Light Wavelength
- Duration of Light
- Carbon Dioxide
Since photosynthesis cannot takes place in the dark, thus light is the most important factor in determining the rate of photosynthesis.
Since, the plant uses only 1.5% of light striking it thus, increasing light up to a certain level is not a limiting factor. And the no matter, how much carbon dioxide and optimum temperature are present, without light, photosynthesis cannot take place.
In the light-dependent reaction, with an increase of light intensity, the no. of photons generated by light increases thus, the ionization of chlorophyll molecule increases and more energy currency molecules can be produced thus, increase in photosynthesis.
But with further increases in light intensity can cause chlorophyll damage, thus the rate of reaction decreases.
And at the light intensity where, the temperature of the plant increases, which results in increased transpiration and closing of stomata as a reaction to it, will lead to a decrease in carbon dioxide uptake and a permanent halt in photosynthesis.
Since light-independent reactions, do not use light for photosynthesis, thus they show no change in the rate of photosynthesis.
The wavelength at which, light is striking the chlorophyll molecule is also important as PS1 absorbs maximum at 700 nm and PS2 absorbs maximum at 680nm, thus light of this wavelength will show maximum rate. An experiment conducted by Engelmann showed that the maximum rate of photosynthesis can be seen at red and blue wavelengths.
Duration of light
As long as the temperature of the plant remains constant, thus the longer the light strikes the leaf surface, the more photosynthesis can be seen.
- It affects the light-independent reaction, as with the increasing rate of carbon dioxide, the amount of its incorporation into the carbohydrate increases and shows the sudden rise in the rate of photosynthesis.
- But further increase can be limited by other factors.
- As carbon dioxide is low in the atmosphere, thus it rise can affect the rate of photosynthesis with great intensity.
- Light-dependent reactions use light for photosynthesis, thus they show no change in the rate of photosynthesis with an increase in temperature.
- Thus, the increasing temperature only affects light-independent reactions.
- Since, light-independent reaction utilizes the activity of an enzyme, thus with an increase in temperature, as the temperature reaches an optimum temperature at which those particular enzymes show the highest catalysis activity, thus, rate of photosynthesis increases.
- But, with a further increase in temperature, some enzymes might get denature, thus the rate of photosynthesis stops.
- During the dehydration conditions, stomata close to reducing the loss of water during transpiration, this further results in lower carbon dioxide intake and photosynthesis stops.
- Thus, it directly affects the rate of photosynthesis and is one of the most important factors.
- The rate of photosynthesis is most favored by the optimum level of oxygen. Thus, in C3 plants, oxygen is required for photorespiration and which results in the formation of CO2 as a byproduct, which is an important factor in the rate of photosynthesis.
- For the process of photosynthesis, the energy produced b=by oxygen respiration is required. But, further increase in concentration can disrupt the intermediaries of photosynthesis and thus can halt the process of photosynthesis.
- A higher concentration of oxygen also completely inhibits the CO2 binding with RUBISCO which is an important enzyme in the process of photosynthesis.
Photosynthesis Law of Limiting Factors
- Formulate by Blackmann in 1905.
- According to this law, The factor which is shortest in supply can limit the rate of photosynthesis. Thus comprehend that when there is more than one factor in the process of photosynthesis, the rate is mostly affected by a factor that has a minimum supply.
- For example, there is no photosynthesis, if there is no light. And when the light intensity began to increase, the photosynthesis increases. But the further increase in photosynthesis increases the temperature of the plants, and thus, photosynthesis stops.
- The graph is showing an example of low carbon dioxide concentration.
- The rate of photosynthesis at lower carbon dioxide is lower, even if there is an optimum light intensity to support the process of photosynthesis, thus the graph plateaus. And it acts vice versa in a sense, that if there is a high amount of carbon dioxide concentration, but low light intensity thus reaction plateaus.
- If both are high in concentration, the temperature comes into the picture and acts as a limiting factor, and again rate plateaus.
- Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. Photosynthesis. Available from: https://www.ncbi.nlm.nih.gov/books/NBK9861/