Essay on the Carbon Cycle

After reading this essay you will learn about the carbon cycle.

Carbon is a common constituent of all organic matter (plant and animal residues). Carbon is continually being fixed into organic form by photosynthetic organisms under the influence of light and once bound, the carbon becomes unavailable for use in the generation of new plant life.

Therefore, it is essential for the carbonaceous materials to be decomposed and returned to the atmosphere for the survival of the higher organisms.

The decomposition of plant and animal remains in soil constitutes a basic biological process in that carbon (C) is re-circulated to the atmosphere as CO₂, nitrogen (N) is made available as NH₄⁺ and NO₃^– and other associated nutrient elements like P, S, Fe, Mn, Cu and Zn etc. appear in plant available forms.

In the process, part of the nutrient elements is assimilated by micro-organisms and incorporated into microbial tissues (soil biomass). The conversion of organic forms of C, N, P and S to inorganic or mineral forms is called mineralization and the conversion of inorganic forms of those elements to their organic forms is known as immobilization.

The carbon cycle revolves about CO₂ and its fixation and regeneration. Chlorophyll containing plants utilize the gas as their sole carbon source, and the carbonaceous matter thus synthesized serves to supply the animal world with preformed organic carbon. Upon the death of the plant or animal, microbial metabolism assumes the dominant role in the cyclic sequence.

The dead tissues undergo decay and are transformed into microbial cells and a large amount of heterogeneous carbonaceous compounds together known as humus or as the soil organic fraction. The cycle is completed and caron made available with the final decomposition and production of CO₂ from humus and the rotting tissues.

The carbon cycle is shown below (Fig. 19.4):