Factors Affecting Photosynthesis - 2 | Agriculture Optional Notes for UPSC PDF Download

Blackman’s Principle – Major Limiting Factor for Photosynthesis

Blackman's Principle, also known as the Law of the Minimum, is a fundamental concept in biology that explains how the rate of a physiological process is restricted by the factor that is in shortest supply. This principle was established by F.F. Blackman in 1905 while studying the factors influencing photosynthesis. Blackman's Principle essentially states that in processes relying on multiple factors, the rate of the process is dictated by the slowest factor, or the one that is least favorable, which limits the overall rate.

• Plant Growth Example: To illustrate Blackman's Principle, imagine a potted plant that requires various factors for growth, such as sunlight, water, nutrients, temperature, and carbon dioxide. If all these factors are abundant except for water, then water becomes the limiting factor. Regardless of the surplus of sunlight, nutrients, or carbon dioxide, the plant's growth will be constrained by the insufficient water supply.
• Relevance to Photosynthesis: Blackman's Principle holds significant relevance in the context of photosynthesis, a process influenced by factors like light intensity, carbon dioxide levels, temperature, and water availability.
• Photosynthesis Example: Let's consider a scenario where a plant is exposed to ample sunlight and has an abundant water source, but the concentration of carbon dioxide in its surroundings is low. In this case, the rate of photosynthesis will be constrained by the limited carbon dioxide concentration. Even if light intensity is increased, photosynthesis won't accelerate as carbon dioxide is the limiting factor.
• Temperature's Role: Similarly, extremely low temperatures can limit photosynthesis. Even with high light intensity and sufficient carbon dioxide, the rate of photosynthesis will be restricted by temperature. This is because the enzymes involved in photosynthesis function optimally at specific temperatures, and their efficiency diminishes at lower temperatures.
• Agricultural Application: Farmers and agricultural experts can utilize Blackman's Principle to their advantage by identifying the limiting factor in a given environment. By adjusting conditions to alleviate the limitation, they can optimize the rate of photosynthesis and subsequently enhance crop yields. For instance, in a greenhouse, if low carbon dioxide concentration is identified as the limiting factor, it can be artificially increased to boost the rate of photosynthesis.

Other Factors that Affect the Process of Photosynthesis

In addition to the previously discussed factors, there are several other elements that can have an impact on the process of photosynthesis. These factors encompass minerals, air pollutants, and specific chemical compounds. The rate of photosynthesis is influenced by a complex interplay of both internal and external factors, making it essential to comprehend these elements and their consequences on photosynthesis, especially concerning agriculture and horticulture.

• Minerals: Numerous minerals are indispensable for plant growth and are closely intertwined with the processes of photosynthesis. Among these minerals are magnesium, iron, copper, chlorine, manganese, and phosphorus. For instance, magnesium is a fundamental component of chlorophyll, while iron participates in chlorophyll synthesis. A deficiency in these minerals can lead to a reduction in chlorophyll content, thereby impacting the rate of photosynthesis.
• Air Pollutants: Airborne pollutants, such as ozone, sulfur dioxide, and hydrogen fluoride, have the capacity to diminish photosynthetic activity. These pollutants have the potential to harm leaf tissue and obstruct light absorption, subsequently reducing the rate of photosynthesis. Extended exposure to these pollutants can result in chronic damage and substantially impede plant growth and productivity.
• Chemical Compounds: Certain chemical compounds, even in trace amounts, can depress the rate of photosynthesis by inhibiting the enzymes involved in the process. For example, substances like hydrogen cyanide and hydrogen sulfide can hinder the activity of specific enzymes, consequently affecting photosynthesis's pace. Likewise, chloroform and ether can impede photosynthesis, and at elevated concentrations, these compounds can induce cell death.