In 1843, the scientist Liebig said, if a physiological process is controlled by more than one effector, the rate of the process will be controlled by the slowest effector. This is called Law of minimum. In 1905, F. F. Blackman expanded the Law of Minimum to determine the Law of Limiting Factor. He said, when a biochemical reaction is influenced by more than one effector, the rate of the reaction is determined by the effector of the lowest magnitude. This formula is called Law of Limiting Factor. The lesser factor is called Limiting Factor. The formula is called Blackman’s Law of Limiting Factor after him.
Explanation: According to the principle of limiting factors, each factor of photosynthesis has an optimum value. Another factor controls the rate of the process when the optimum value is exceeded.
30-350C is the optimum temperature for photosynthesis. As the temperature gradually increases from 00C, the rate of photosynthesis also increases and peaks at 30-350C. But when the temperature is raised above 350C, the rate of photosynthesis suddenly decreases rapidly. Another effector then controls the rate of photosynthesis.
Again, the optimum value of leaf CO2 utilization per hour for photosynthesis is 10 mg. As the level of CO2 utilization gradually increased from 1 mg, the rate of photosynthesis also increased and peaked at 10 mg. But when CO2 is increased above 10 mg, the rate of photosynthesis suddenly drops rapidly. Another effector then controls the rate of photosynthesis.
As can be seen from the diagram, according to the principle of Limiting Factor, if the rate of photosynthesis is controlled by several factors at the same time, the amount of any one effector indicates the steady state of photosynthesis.