Page 61 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 49

microorganisms are finally changed into inorganic N that can be absorbed by plant
roots after encountering decompotsition processes. A part of the inorganic N also
volatilizes to the atmosphere, particularly in a reductive condition. All the
+
-
processes of N transformation from N 2 in the atmosphere to NH 4 and NO 3 , and
then their absorption by plant roots and transformation to be structural and
functional substances in plant tissues and microorganisms, and then their ultimate
-
+
decomposition back to form inorganic N (NH 4 and NO 3 ) that are available to plants
makes a cycle. This cycle is called Nitrogen Cycle or N-Cycle as shown in Fig. 4.9.

N 2

NH 3
NH 4 +

NO 2 -

(Fixation/Decomposition)
Microorganisms NO 3 -
PROTEASES

Plants
Organic N

(Protein) (Proteins)
Animals/ Plants
Humans

Fig. 4.9. The N Cycle (Adapted from Salam, 2012).

The organisms that can fix the atmospheric N is the Nitrogen Fixing Bacteria;
so-called due to their ability to fix and incoorporate atmospheric N into their
bodies. A part of these bacteria such as Rhizobium sp. lives symbiotically with
particular plant roots. Legumes and peanuts are two of these particular plants. In
this symbiosis, plants supply nutrients and water needed by bacteria, while
bacteria supply N for plants. In addition to these bacteria that live symbiotically,

Abdul Kadir Salam - 2014