Page 76 - Enzymes in Tropical Soils

64 Enzymes In Tropical Soils

by organisms involving its reverse reaction called respiration. During the
respiration CH 2 O is decomposed into H 2 O, CO 2 , and energy. Hydrocarbons may be
present in various forms. Bohn et al. (1985) listed some forms of organic matters
as shown in Table 5.2.
Plant roots, macroorganisms, and microorganisms use O 2 as the main
electron acceptor. In the absence of O 2 , both plant roots and macroorganisms can
not oxydize hydrocarbon bacause no chemical species will accept electrons
released during the oxydation of hydrocarbon. However, soil microorganisms may
continue the oxydation of hydrocarbon by employing some chemical species in
soils as electron acceptors. Using any of these acceptors, soil microorganisms will
obtain less energy and, consequently, conduct less activities. Bohn et al. (1985)
showed some of these electron acceptors as listed in Table 5.3.

Table 5.2. Some hydrocarbons as sources (electron donors) of
energy for soil organisms.

1 Organic Matter Lignin (C2.8H2.9O)
(Individual) Cellulose (C2.2H2O)
(Dry/Fresh)
2 Litters (1/3 Lignin 2/3 Cellulose)
+
4+
C 1.7 H 2.2 O  1.7C + H 2 O + 0.2 H + 7e -
-
4+
3 Organic Matter C 2.2 H 2.2 O  2.2C + H 2 O + 0.2 OH + 9e -
(whole)
After Bohn et al. (1985)

The above explanation suggests that the highest energy obtained by soil
microorganisms occurs when O 2 is used as the electron acceptor, as also used by
plants roots and soil macroorganisms. In this situation, soil microorganisms may
progressively develop their populations and increase their activities (Yusnaini et al.,
2007). Their activities may be measured, among others, by measuring the CO 2
evolution and also enzymatic activities (Salam et al., 1998d; 1999d; 1999e; Yusnaini
et al., 2007). The increase in the evolution of CO 2 as a result organic matter
addition is shown in Table 5.4. Hellmann et al. (1997) reported that the emission
rates of carbondioxide (CO 2 ), and also methane (CH 4 ) and nitrous oxide (N 2 O),
increased successively during compost maturation. Green manure and Chicken
Manure significantly increased the activities of soil microorganisms as shown by the
increase in CO 2 evolution. The effect of the Chicken Manure was also shown to be

Abdul Kadir Salam - 2014