What is the Biogeochemical Cycle

What is the Biogeochemical Cycle

Biogenic elements (macro-, micro- & other elements) flow from the environment into and out of the plant in a cyclic manner.
This flow of nutrients from abiotic to biotic components of the ecosystem and vice-versa constitute the biogeochemical cycles.

Hydrological or Water Cycle :

• Water on earth is cycled by two processes, evaporation and precipitation.
• The atmospheric precipitation occurs in the form of snow, hail or sleet etc. The run off water is finally collected in ocean through rivers.
• Some water remains solid in the form of snow which gradually melts and reaches the sea.
• Soil water is used by plants and most of it again reaches the atmosphere through transpiration.
• Animals consume water directly from water bodies & also the gravitational water.
• By evaporation, the water returns to atmosphere and cycle is repeated.

Carbon Cycle :

• CO₂ is 0.03% in atmosphere, which is utilized by producers in photosynthesis for making food.
• From producers, it goes to consumers and then through decomposers into atmosphere.
• The producers, consumers & decomposers may be converted into fossil fuel (petrol, coal etc.) or form carbonate rock after death.
• By way of respiration the biotic component returns CO₂ to atmosphere.
  
• CO₂ may get dissolved in water. The lime rocks also contribute to CO₂ in water. The aquatic producer use this CO₂ for photosynthesis and return it by respiration.
• By combustion of fossil fuel & also by volcanic activity, CO₂ is returned to the atmosphere.

Nitrogen Cycle :

• The atmosphere is the source of N₂ where it is about 79%. Plant cannot use N₂ directly.
• In living organisms nitrogen is important constituent of protein and nucleic acid.
• The N₂ cycle has five important steps –
  1. Nitrogen Fixation :
     Conversion of N₂ gas into its compounds like nitrates & nitrites is called N₂ fixation. It is done either non-biologically by lightening or biologically by symbiotic or free- living bacteria. O₂ is harmful for N₂fixing bacteria.
  2. Assimilation of Nitrogen :
     N₂ cannot be used by plants directly. They absorb it in the form of nitrate. Nitrate later on reduced to ammonia which provide amino (–NH₂) group. It is important part of proteins.
  3. Ammonification :
     Dead plant & animal protein and their waste like urea & uric acid converted to ammonia by some ammonifying bacteria in soil. e.g.  Bacillus mycoides, B. vulgaris & B. ramosus etc.
  4. Nitrification :
     Ammonia is converted into nitrite by Nitrosomonas bacteria, and Nitrobacter convert nitrite into nitrate. This nitrate again can be absorbed by plant & thus cycled back.
  5. Denitrification :
     Some denitrifying bacteria like Pseudomonas reduce nitrate into nitrogen gas in soil. This gas is again back to environment.