Carbon CycleDate: 22-9-2021
Growing plants depend on carbon dioxide in the air for their daily carbon intake. Plants assimilate a small quantity of carbon from carbonates and bicarbonates absorbed from the soil solution. They transform this carbon so it can be used in complex compounds in the form of tissues. As atmosphere is deprived of its carbon dioxide, it is almost simultaneously replenished by CO2 liberated by decaying plant and animal remains. A small amount of CO2 is excreted by plant roots as well. Eventually, the CO2 passes from the soil where it is produced to the atmosphere to be utilized again by the plants.
Higher animals and soil micro-organisms depend mainly upon the highly organized plant tissues and plant products for their carbon requirement as they cannot utilize atmospheric CO2. A part of the carbonaceous substances like cellulose, hemicellulose, lignin, fats, waxes etc., that cannot be digested and assimilated in the animal body is excreted in the form of dung and urine. The excretory products get mixed with the soil or are converted into farmyard manure and compost, where they undergo decomposition and again liberate CO2.
Same is the case with micro-organisms. Some of them are autotrophs which take atmospheric carbon just like higher plants, while heterotrophic micro-organisms obtain their carbon by breaking down complex organic substances. Majority of soil micro-organisms are heterotropic and depend on plant and animal tissues in the soil to fulfill their carbon requirement. They utilize a part of the liberated carbon to build their own body tissues and convert the rest to CO2. This CO2 diffuses rapidly into the atmosphere from where it is absorbed by growing plants and other autotrophic organisms. When the micro-organisms complete their life processes and die, their remains and residues get mixed with the soil, only to be decomposed by the soil micro-organisms again.
The carbonaceous products of plant metabolism are utilized by animals for their nutrition. The excretory products of animals, remains of animals and plants are utilized by micro-organisms for their carbon requirement, while the gaseous by product of the metabolic activities of micro-organism serves as a source of carbon for plants. The change in the form of CO2 is a continuous cycle from gaseous atmospheric CO2, to highly complex carbonaceous compounds and then reconversion of these substances back to CO2 through plants, animals and micro-organisms. This is the circle of life and every organism is an important part of it.
- Vijaykumar M. Sarur
Kothari Agritech Pvt Ltd