Law of Limiting Factor

Limiting factors are the factors that are not present in abundance. These are the environmental conditions or resources that limit the growth or distribution of an ecosystem. These can be either physical or biological factors which are identified by the increase or decrease in growth or distribution of a population.

Blackman’s Law of Limiting Factors

• A plant physiologist Blackman studied limiting factors in the photosynthesis system of plants. He stated that biological factors are affected by a number of factors, but the amount in which they affect the whole process is different. Let us take the example of photosynthesis. Plants require adequate amounts of water, sunlight, chloroplast, temperature, carbon dioxide and chlorophyll to carry out photosynthesis. The scarcity of any of these components will affect the process of photosynthesis.
• Any physiological process which is affected by more than one factor is governed by the law of limiting factors.
• The relative magnitude of factors is more important than the absolute magnitude.
• A factor which is present in less quantity is the limiting factor.
• When the rate of the process becomes constant due to a limiting factor, it can be regulated by regulating the amount of the factor only which is limiting. For eg., a leaf which can utilize 5mg of CO₂ per hour in photosynthesis is exposed to certain light intensity. If only 1mg of CO₂ enters the leaf in an hour, the rate of photosynthesis is limited due to the CO₂ factor. As the concentration of CO₂ increases, the rate of photosynthesis is also increased. Any further increase in the CO₂ concentration will not affect the rate of photosynthesis. It will only increase if the intensity of light is increased.

Criticism of Law of Limiting Factors

While explaining the principle of limiting factors, Blackman exhibited abrupt breaks in the rate of photosynthesis due to the low intensity of light. According to his coworkers, the rate of photosynthesis does not decline abruptly, but gradually, whenever a factor is limiting.

This is because all the chloroplasts are not under similar environmental conditions. The exposed ones receive more light and CO₂ than the deep-seated ones. If these factors are limiting, the photosynthesis will be affected only in some chloroplasts. As a result, the photosynthesis rate will decline gradually.

Also read: Photosynthesis, Chlorophyll, and Chloroplast

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