How do temperature, light intensity, and carbon dioxide concentration act as limiting factors on the rate of photosynthesis?

Sourav PanNovember 8, 2024

Answered

Temperature, light intensity, and carbon dioxide concentration are critical limiting factors that influence the rate of photosynthesis. Each of these factors affects the photosynthetic process in distinct ways, and understanding their roles is essential for optimizing plant growth and productivity.

1. Temperature

• Enzyme Activity: Photosynthesis is largely driven by enzymes, which are sensitive to temperature changes. As temperature increases, the kinetic energy of molecules rises, leading to more frequent collisions between enzymes and substrates, thus increasing the reaction rate. However, this increase continues only up to a certain point.
• Optimal Range: Each plant species has an optimal temperature range for photosynthesis. Beyond this range, particularly at high temperatures, enzymes can denature, leading to a decrease in the rate of photosynthesis as the enzyme’s functional structure is compromised. For example, plants acclimated to cooler temperatures will have lower optimal photosynthetic rates compared to those adapted to warmer climates.

2. Light Intensity

• Photon Absorption: Light is essential for the light-dependent reactions of photosynthesis, where chlorophyll absorbs photons to convert light energy into chemical energy (ATP and NADPH). As light intensity increases, more chlorophyll molecules are activated, enhancing the rate of photosynthesis.
• Saturation Point: However, there is a saturation point where all available chlorophyll is fully utilized. Beyond this point, further increases in light intensity do not enhance the rate of photosynthesis because other factors (such as CO₂ concentration or temperature) may become limiting. Additionally, excessive light can lead to photoinhibition, where too much light energy damages the photosynthetic apparatus.

3. Carbon Dioxide Concentration

• Carbon Fixation: CO₂ is a crucial substrate for the Calvin cycle, where it is fixed into organic molecules. As CO₂ concentration increases, the rate of photosynthesis generally rises because more carbon can be incorporated into glucose and other carbohydrates.
• Plateau Effect: Similar to light intensity, there exists a threshold beyond which additional increases in CO₂ concentration do not further enhance the rate of photosynthesis. This plateau occurs when enzymes responsible for carbon fixation become saturated with CO₂