Page 60 - Enzymes in Tropical Soils

48 Enzymes In Tropical Soils

2-
SO 4
NUTRIENTS

SOIL MICROORGANISMS PLANTS
(DECOMPOSERS) (PRODUCERS)

ARYLSULPHATASE

ANIMALS
ORGANIC S
(CONSUMER I)

ANIMALS
(CONSUMER II)

Fig. 4.8. The cycle of S in the soil – plant system.

4.6 Enzymes in the Cycling of Nitrogen and Urea
Hydrolisis

Nitrogen is, like C, originated from atmosphere. The atmosphere actually
contains various gases, among which it contains 78% N 2 . However, atmospheric N 2
is not available to plants. Unlike C, which is absorbed by plants as CO 2 directly from
the atmosphere through leaf or stem stomata, N can be absorbed by plant roots in
a particular form after encountering reatively long processes. Atmospheric N
initially enters the bodies of bacteria and particular plant roots in the soil – plant
system through a process called N Fixation. The bacteria involved in the fixation
are called Nitrogen Fixing Bacteria (Rendig and Taylor, 1989). Among this bacteria
there is Rhizobium sp. that lives symbiotically with the roots of legumes.
-
+
Nitrogen in N 2 is finally changed to be NH 4 and NO 3 , which are available for
plant root absorption and are utilyzed by plants to form various structural and
functional substances. These structural and functional N in plant tissues and in

Abdul Kadir Salam - 2014