Page 47 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 35

susceptibility to decomposition by proteases – enzymes that accelerate the
decomposition of enzyme proteins.

a. Roles of Soil Microorganisms

Some reports noted that soil microorganisms are the most important
enzyme producers in soils (Duxbury and Tate III, 1981; Ross and Cairns, 1982;
Frankenberger, Jr. and Dick, 1983; Jha et al., 1992; Joner and Jakobsen, 1995;
Naseby and Lynch, 1997; Vinotha et al., 2000). The role of soil microorganisms in
producing soil enzymes was demonstrated by Salam (1998a). In the absence of
macroorganisms and plant roots, Salam (1998a) treated an air-dry soil sample with
distilled water from 0 to 20 – 120%. The activity of phosphatase was measured
after a one week incubation at room temperature. The result is shown in Fig. 4.1.
The activity of phosphatase increased in the presence of water of 20 – 40% with a
maximum at 40%. The activity of phosphatase then decreased after the maximum
activity and the lowest was found at the highest water addition of 120%.

160
150

140
Activity of Phosphatase (mg p-Nitrophenol g -1 h -1 ) 120
130

110

100
90
80
0 20 40 60 80 100 120
Water Content(%)

Fig. 4.1. Effect of soil water on the phosphatase activity
(Salam, 1998a).

Abdul Kadir Salam - 2014