Page 68 - Enzymes in Tropical Soils

56 Enzymes In Tropical Soils

4.8 Factors Affecting the Soil Biochemical Reactions

As previously explained for enzymes in general terms, the rates of soil
biochemical reactions are also controlled by at least four factors involving abiotic
and biotic factors (Baligar et al., 1988; Rejsek, 1991; Salam et al., 1997d; Wu et al.,
2012). The first abiotic factor is the presence and the amount of substrate in the
soil system, which is represented by organic matters. A direct relationship
between the activities of soil enzymes and soil organic C or organic matter contents
and total N (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;
Salam et al., 1998d; Wu et al., 2012) supports this theory.
The second abiotic factor controlling the rates of soil biochemical reaction is
the amount of enzymes in soils. With the increase in the amount of substrate in
soils, the rate of soil biochemical reactions is more dependent on the available
catalysts, that decreases the energy of activation of the biochemical reaction. The
rates of the biochemical reaction may increase with the increase in the
concentration of soil enzymes. Therefore, all factors controlling the activity of soil
enzymes will then enhance the rates of the soil biochemical reactions.
The third abiotic factor controlling the rates of the soil biochemical reactions
is soil water content (Wu et al., 2012). Water is important due to its role as a
reactant in the hydrolysis process involved in the soil biochemical reactions. In dry
soils, the hydrolysis of organic matter does not occur due to the absence of water.
In general, the rates of soil biochemical reactions increases with the increase in soil
water content until a particular value, after which further addition of water will
decrease the rates of soil biochemical reactions (Klein and Koths, 1980; Salam,
1998a).
The fourth abiotic factor affecting the rates of soil biochemical reactions is
soil temperature (Harrison, 1983; Neal, 1990). The soil temperature affects the
rates of the soil biochemical reaction through at least two mechanisms. First is a
direct effect of temperature on the microorganisms producing soil enzymes. At
low temperature, the populations and activities of soil microorganisms are low and,
hence, produce low enzymes. The populations and activities of microorganisms
and also the production of enzymes may increase with the increase in soil
temperature. The second is a direct effect of soil temperature on the soil
enzymatic reactions. The rates of biochemical reactions generally increase with the

Abdul Kadir Salam - 2014