In this factors affecting photosynthesis in plants post we have briefly explained about environmental or external factors affecting photosynthesis and internal factors affecting photosynthesis.
Factors Affecting Photosynthesis in Plants
In 1860, Sachs gave three cardinal points theory explaining minimum, optimum and maximum factors that control photosynthesis. In 1905, Blackman put forth the importance of smallest factor. Blackman’s law of limiting factor is actually a modified Law proposed by Liebig’s Law of minimum.
According to Blackman, “When a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the lowest factor”. To conclude in an easy way “at any given point of time the lowest factor among essentials will limit the rate of photosynthesis”.
For example, when even sufficient light intensity is available, photosynthesis may be low due to low CO2 in the atmosphere. Here, CO2 acts as a limiting factor. If CO2 is increased in the atmosphere the rate of photosynthesis also increases. Further increase in photosynthesis is possible only if the available light intensity is also increased proportionately.
Factors affecting photosynthesis are further grouped into external factors affecting photosynthesis and internal factors affecting photosynthesis. I. External factors affecting photosynthesis : Light, carbon dioxide, temperature, water, mineral and pollutants. II. Internal factors affecting photosynthesis: Pigments, protoplasmic factor, accumulation of carbohydrates, anatomy of leaf and hormones.
External Factors Affecting Photosynthesis
Energy for photosynthesis comes only from light. Photooxidation of water and excitation of pigment molecules are directly controlled by light. Stomatal movement leading to diffusion of CO2 is indirectly controlled by light.
Intensity of light an external factors affecting photosynthesis plays a direct role in the rate of photosynthesis. Under low intensity the photosynthetic rate is low and at higher intensity photosynthetic rate is higher. It also depends on the nature of plants. Heliophytes (Bean Plant) require higher intensity than Sciophytes (Oxalis). In plants which are exposed to light for longer duration (Long day Plants) photosynthetic rate is higher.
Different wavelengths of light affect the rate of photosynthesis because pigment system does not absorb all the rays equally. Photosynthetic rate is maximum in blue and red light. Photosynthetically Active Radiation (PAR) is between 400 to 700 nm. Red light induces highest rate of photosynthesis and green light induces lowest rate of photosynthesis Light
CO2 is found only 0.3 % in the atmosphere but plays a vital role an important external factors affecting photosynthesis. Increase in concentration of CO2 increases the rate of photosynthesis (CO2 concentration in the atmosphere is 330 ppm). If concentration is increased beyond 500ppm, rate of photosynthesis will be affected showing the inhibitory effect.
The rate of photosynthesis decreases when there is an increase of oxygen concentration an another external factors affecting photosynthesis . This Inhibitory effect of oxygen was first discovered by Warburg (1920) using green algae Chlorella.
The optimum temperature for photo synthesis varies from plant to plant another one external factors affecting photosynthesis. Temperature is not uniform in all places. In general, the optimum temperature for photosynthesis is 25C to 35C. This is not applicable external factors affecting photosynthesis in all plants. The ideal temperature for plants like Opuntia is 55C, Lichens 20C and Algae growing in hot spring photosynthesis is 75C. Whether high temperature or low temperature it will close the stomata as well as inactivate the enzymes responsible for photosynthesis.
Water also an external factors affecting photosynthesis. Photolysis of water provides electrons and protons for the reduction of NADP, directly. Indirect roles are stomatal movement and hydration of protoplasm. During water stress, supply of NADPH is affected.
Deficiency of certain minerals also an external factors affecting photosynthesis e.g. mineral involved in the synthesis of chlorophyll (Mg, Fe and N), Phosphorylation reactions (P), Photolysis of water (Mn and Cl), formation of plastocyanin (Cu).
Air pollutants have a negative impact on plant growth, primarily through interfering with resource accumulation an crucial external factors affecting photosynthesis. Once leaves are in close contact with the atmosphere, many air pollutants, such as O3 and NOx, affect the metabolic function of the leaves and interfere with net carbon fixation by the plant canopy.
Internal Factors Affecting Photosynthesis
Pigments are an important internal factors affecting photosynthesis. It is an essential factor and even a small quantity is enough to carry out photosynthesis. Chlorophyll, the primary pigment used in photosynthesis, reflects green light and absorbs red and blue light most strongly. In plants, photosynthesis takes place in chloroplasts, which contain the chlorophyll.
Photosynthetic end products like carbohydrates are accumulated in cells and if translocation of carbohydrates is slow then this will be an crucial internal factors affecting photosynthesis.
Another important internal factors affecting photosynthesis is leaf anatomy. Leaf anatomy may influence net leaf photosynthesis to a large degree and thus cause great differences in light-use efficiency. Like the root and stem, the leaf consists of vascular, parenchymatous and dermal tissue, the latter being a persistent epidermis.
Another important internal factors affecting photosynthesis is hormones. Cytokines and gibberellins increase the rate of photosynthesis but abscisic acid reduces the same.
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