Page 69 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 57

increase in soil temperature until a particular value, after which the rates decrease
with soil temperature. At high temperature, soil enzyme proteins are denatured
and enzyme activities are lower. This condition will lower the rates of the soil
biochemical reactions.
In addition to the above factors, the rates of soil biochemical reactions are
controlled by soil pH (Malcolm, 1983; Reddy et al., 1991; Trasar-Cepeda et al.,
1991; Salam et al., 1998d; 1998i). For example, the activity of phosphatase
(indicating the rates of soil biochemical reaction releasing ortophosphates from
organic P) is reported to be dependent on soil pH (Frankenberger and Johanson,
1982; Garcia et al., 1993). In general, the activity of phosphatase increases with
the increase in soil pH until an optimum pH where the phosphatase activity is
maximum and then decreases after which (Frankenberger and Johanson, 1982;
Trasar-Cepeda and Carballas, 1991; Sakai and Tadano, 1993; Huang et al, 1995;
Salam et al., 1998d).
Some workers also reported the effect of some soluble element in soil water
on the rates of the soil biochemical reactions, among which is the effect of P on the
activity of phosphatase. The majority of researchers reported that the addition of
phosphates into soils decreased the activity of phosphatase (Juma and Tabatabai,
1977; Pang and Kolenko, 1986; Fox and Commerford, 1992). This phenomenon
suggests that fertilizing soils with P fertilizers may lower the biochemical
transformation of organic P into inorganic P. Pang and Kolenko (1986) also found
that the activity of phosphatase in soils decreased by urea treatment.
Among the most important biotic factors are the presence of
microoganisms, earthworms, and plant roots, that produce most of the soil
enzymes. Yusnaini et al. (2007) suggested that the soil microorganisms were the
producers of enzymes in soils. They showed an increasing pattern in CO 2 evolution
due to addition of green and chicken manures. The pattern was similar to the
increase in the activities of alkaline phosphatase and -glucosidase as green
manure or chicken manure was increased. Since CO 2 evolution indicates the
population and activity of soil microorganisms, this correlation suggests that the
soil microorganisms are the producers of alkaline phosphatase and -glucosidase.
As previously stated, it has been reported that the activity of phosphatase in
soils inhabited by earthworms was higher than that in the control soil (Ross and
Cairns, 1982; Satchell and Martin, 1984). The activity of phosphatase in forest soils
were reported to be higher than those in agriculture lands (Salam et al., 1997c;
1998d), in which the population of eartworms were probably lower.
Several reasearches also reveal that plant species greatly affects the activity
of soil enzymes (Duxbury and Tate III, 1981; Jha et al., 1992; Salam, 1996;

Abdul Kadir Salam - 2014