Factors Affecting Photosynthesis

Introduction

Photosynthesis is defined as the process by which plants produce and utilise nutrients by using artificial light or natural sunlight. 

Light energy is converted into chemical energy in the form of sugars and glucose. Glucose molecules and sugars are created from water and carbon dioxide and the oxygen that we breathe is released along with it as a by-product. 

Four Important factors that affect the rate of photosynthesis are the light intensity , the temperature levels, water and CO2. Other factors that can affect the rate of photosynthesis include the leaf anatomy, weather conditions, the age of the leaf, the quality and natural contents in the soil, the chemicals present in the fertilisers and pesticide and conditions that may be unique to the particular plant. Any disbalance in any of these factors can damage a plant in many ways.

Effect of Light Intensity on Photosynthesis

Light intensity in the context of photosynthesis is usually defined as the amount of energy in the form of photons that hits an area of a leaf over a certain period of time. 

Higher light intensity would mean more photons hitting the surface of the leaf. As the number of photons hitting the surface of the leaf increases, the rate of photosynthesis increases, simply because then there is more light available to increase the rate of photosynthesis. However, once this high light intensity reaches a certain point, the rate will not increase further. That is because other factors will start interfering and will either inhibit, stop or lower the rate. 

One such limiting factor can be the number of chlorophyll molecules that absorb light. At extremely high intensities of light, the rate of photosynthesis starts reversing and slows down. The light even starts to damage the plant to a certain level. On the other hand, if the amount of light is too little, photosynthesis cannot possibly occur and the plant would wither without any glucose or sugar production. There are numerous complicated interactions between plants and light other than photosynthesis.

Blue and red light is said to be the most effective because photosystems most optimally absorb light that contains wavelengths between 680 nm and 700 nm (nanometers).

Effect of Temperature on Photosynthesis

The rate of photosynthesis is also dependent on the temperature. The higher the temperature is, the higher the rate of photosynthesis is. 

We all know that photosynthesis is mainly a chemical reaction and chemical reactions usually tend to increase in their reaction rate as the temperature increases. However, for the process of photosynthesis, it does not indefinitely increase in all circumstances. Any temperature above 40°C will start to decrease the rate of photosynthesis. This reduction is a result of enzymes being involved in chemical reactions. These enzymes are temperature sensitive and at high temperatures, they stop operating and get altered naturally. For low temperatures, it is restricted by the number of molecular collisions taking place between the substrate and the enzymes.

It is important to keep the temperature range between 25°C and 35°C for an optimal rate of photosynthesis to take place.

Other Factors Affecting the Rate of Photosynthesis

Other than light intensity and temperature intensity, there are some other factors as well that can affect the process of photosynthesis. These include the concentration of oxygen, carbon dioxide, nitrogen and the levels of air pollution present in the environment. 

• Oxygen: Oxygen is needed to break the various sugars into carbon dioxide and release energy that the plants use to stay alive. Low oxygen levels and environments tend to decrease the absorption, which may lead to the inhibition and lower rates of photosynthesis.

• Carbon dioxide: An increase in carbon dioxide concentrations also increases the rate at which carbon is incorporated into carbohydrates in the light-independent photosynthetic reaction, therefore the rate of photosynthesis increases unless it is limited by another factor.The concentration of CO2 in the atmosphere is about 0.036 percent (360 ppm), which is very low as compared to the concentration of other gases in the atmosphere. e.g. O2 about 20 percent and nitrogen nearly 80 percent. The C3 and C4 plants differ in their photosynthetic responsiveness to the available CO2 concentration. In C3 plants, rate of photosynthesis increases with an increase in CO2 concentration (upto at least 500μl.l-1) when other factors are not limiting.   In C4 plants also, photosynthesis increases as the concentration increases. However, the C4 plants attain saturation at much lower CO2 concentration (i.e., around the present level of 360 μl. l-1) than the C3 plants, which become saturated at CO2 levels of about 500 μl. l-1. Thus, the current availability of CO2 in the atmosphere is a limiting factor for C3 plants.  The effects of various levels of carbon dioxide are similar to the case of light intensity, as elaborated in the previous section.

• Nitrogen: More nitrogen supply increases the chlorophyll content, the amount and activity of carboxylation enzymes, protein, sugars and glucose as well as total nitrogen and other photosynthesis-related metabolites.

• Air pollution: Leaves contain ​chlorophyll​ which is responsible for photosynthesis. Photosynthesis is directly affected as the metabolic functions of chloroplasts exposed to air pollution have a lowered ability of fixing carbon.

• Water: Water is an essential raw material in photosynthesis. Under field conditions water may be a limiting factor for photosynthesis not only during prolonged drought periods but also every afternoon, particularly during hot weather. It supplies H+ and electrons in the photochemical phase of photosynthesis. Though less than 1% of water absorbed by a plant is used in photosynthesis, its reduced availability retards the rate of photosynthesis through the closure of stomata. When stomata are complexity closed, photosynthesis may cease. In addition, the decrease in the availability of water leads to dehydration of protoplasm, which ultimately affects the enzymes involved in photosynthesis

Conclusion

Light intensity, temperature and carbon dioxide concentration are some of the main factors that affect photosynthesis. 

Other factors include leaf anatomy, weather, the age of the leaf etc. As we increase the intensity of light, the rate of photosynthesis also increases. However, with too much light, there are other factors that can start limiting the rate of photosynthesis. With too little light, photosynthesis cannot possibly occur and the plant can suffer without any glucose or sugar production. When it comes to heat, the higher the temperature, the higher is the rate of photosynthesis. It is important to keep the range between 25°C and 35° C for the most effective rate. Other than light and temperature intensity, there are factors such as the concentration of carbon dioxide, air pollution and the availability of oxygen that affect the rate of photosynthesis.