Page 74 - Enzymes in Tropical Soils

62 Enzymes In Tropical Soils

matter in soils causes a higher population of earthworms, particularly in moist soils.
Therefore, earthwoms are found more frequently in topsoils rather than in subsoils
due to a higher content of organic matters in topsoils. Yusnaini et al. (2002)
reported that the populations of earthworms were higher in the secondary forest,
shrubs, and alang-alang (Imperata cylindrica) fields compared to those in more
intensively cultivated lands with lower contents of organic matters. Since
earthworms are the producer of alkaline phosphatase, a higher population of
earthworms may cause a higher activity of alkaline phosphatase in soils. Several
workers reported that activities of phosphatases in soils with higher populations of
earthworms were higher than those in the controls (Ross and Cairns, 1982; Satchell
and Martin, 1984). One of the important earthworms is Lumbriscus terrestris
(Edwards and Lofty, 1977). Joner and Jakobsen (1995) also showed that the
activities of acid and alkaline phosphatases were higher in the rhizospere than
those in the bulk soils without plant roots. This phenomenon was related either to
a higher organic matter content in the rhizospere or to a higher production of
phosphatases by plant roots.
The above explanations suggest that organic matter is greatly important for
the producers of soil enzymes. Therefore, organic matter may indirectly affect the
activities of soil enzymes. The higher contents of organic matter in the soil system
may drive higher activities of soil enzymes. A great deal of scientific findings on this
phenomenon has been reported (Klein and Koth, 1980; Nannipieri et al., 1980;
Harrison, 1983; Trasar-Cepeda and Gil-Sotres, 1987; Bonmati et al., 1991; Tate III et
al., 1991; Martens et al., 1992; Salam, 1996; Deng and Tabatabai, 1996; Salam et
al., 1998d; 1999d;1999e; Luo et al.,2010).

5.1 Organic Matters as Sources of Energy for
Microorganisms

The use of organic matter by the living things is a part of a simple carbon
cycle shown in Fig. 5.1. Hydrocarbon is initially produced by the reaction between
carbondioxyde and water molecules during photosynthesis in the chlorophyls of
plant leaves. During this redox reaction, C molecule is reduced with its oxydation
state decreases from +4 in CO 2 (oxydized)to 0 in CH 2 O (reduced) with the sun
energy packed in it; while the oxydation state of O increases from -2 in CO 2
(reduced) to 0 in O 2 (oxydized). The hydrocarbon is finally used by organisms for its
energy by the following reaction called respiration (Eq. 5.1).

Abdul Kadir Salam - 2014