Limiting factors of Photosynthesis of Blackman

 

FACTORS AFFECTING PHOTOSYNTHESIS

Photosynthesis  is  essential to generate the productivity for any ecosystem. The rate of photosynthesis is very important in determining the yield of plants including crop plants. Photosynthesis is influenced by the several factors that may be  both internal and external. The internal factors include the number, size, age and orientation of leaves, mesophyll cells and chloroplasts whereas the internal carbon dioxide concentration and the amount of chlorophyll are also included in internal factors. The external factors are the availability of sunlight, temperature, carbon dioxide concentration and water. Generally several factors interact and  affect the rate of  photosynthesis or carbon dioxide  fixation. Usually one factor is the major cause and that  also  limits the rate of photosynthesis.

When several factors affect any biochemical process of photosynthesis then the  Law of Limiting Factors of Blackman comes into effect. The law of limiting factors of Blackman stated that  If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: For example, if plants have  green leaf and optimal light and CO2 conditions than  the plant do not perform the  photosynthesis if the temperature is very low.  If the optimal temperature is given to the plants then plants will start photosynthesis at its rate. The factors that affect the rate of photosynthesis are as follow- 

Light

The features of light such as light quality, light intensity and the light  duration are important for the rate of photosynthesis and light is a factor that affects the photosynthesis. There is a linear relationship between incident light and carbon dioxide fixation rates at low light intensities. At higher light intensities, the rate does not increase  because other factors  are limited.

The light that  is used  by photosynthesis or saturation of light is only ten percent of the Total  sunlight.

Except for those  plants that are found  in shady or dense forests, light is rarely a limiting factor in nature.  The Increase in  light intensity  beyond a point causes the breakdown of chlorophyll and  decrease the rate of  photosynthesis. 

At low light conditions neither group responds to high CO2 conditions. At high light intensities, both C3 and C4 plants show increase in the rates of photosynthesis.

Carbon dioxide 

Carbon dioxide is the major limiting factor for photosynthesis. The concentration of carbon dioxide in the atmosphere is 0.03  per cent . Increase in concentration of carbon dioxide upto more than this concentration   can increase the rate of fixation of carbon dioxide . 

The C3 and C4 plants provide response in different way  for carnon dioxide concentrations.. The C4 plants show saturation at value of  360 µlL-1 while C3 plants responds the saturation upto 450 µlL-1 .This value reveals that  the current availability of carbon dioxide  is limiting to the C3 plants. The fact that C3 plants gives positive response at the  higher carbon dioxide  concentration. C3 plants show increased rates of photosynthesis and generate the higher productivity.  Some crops such as tomatoes and bell pepper  are allowed to grow in carbon dioxide enriched atmosphere that leads to higher yields. 

Temperature

The enzymes that are involved in dark reactions  are controlled by the temperature and  the enzyme for the light reactions are also sensitive for the temperature. At the higher temprature, The C4 plants  show higher rate of photosynthesis while C3 plants need lower temperature for the the photosynthesis. The range of temperature  for photosynthesis is  different  for the plants and depends on the habitat that they are adapted. Tropical plants are well adapted for the higher temperature  than the plants adapted to temperate climates. 

Water

Water is one of the factors but   the effect of water as a factor is not directly involved in photosynthesis.  Deficiency of Water causes the closing  of stomata. As a result, the CO2 availability is also reduced.The water deficiency also causes the wilting of leaves. As a result, the surface area of the leaves is also reduced and causes a low rate of their metabolic activity.