Page 50 - Enzymes in Tropical Soils

38 Enzymes In Tropical Soils

amylase, urease, and phosphatase. Supriatin et al. (2007) reported that the
population of earthworms and activity of phosphatase in eathworms casts were
greatly influenced by the amount and diversity of organic matters eaten by
earthworms.

c. Roles of Plant Roots

In availing nutrient elements in soils, plant roots also excret some ions and
+ -
organic molecules. In addition to excreting H and OH ions as well as organic acids,
plant roots also excret some enzymes. These enzymes may participate in
accelerating the nutrient element detachment from particular organic molecules.
Because enzymes are specific, various enzymes are produced by plant roots
depending on the need of plants. The amounts of enzymes released by plant roots
are also dependent upon the type of plants and land-use systems. It is clear that as
pointed out by some reasearchers, plant roots are one of the soil enzyme
producers (Duxbury and Tate III, 1981; Reddy et al., 1987; Tate III, 1987; Fox and
Commerford, 1992; Sakai and Tadano, 1993; Joner at al., 1995; Naseby and Lunch,
1997; Fang et al., 2010). For example, Joner et al. (1995) reported that the
activities of acid and alkaline phosphatases were highest on the surface of roots
and lower the further away from root surface of cucumber. This phenomenon is
depicted in Fig. 4.3.
It has been reported that the activities of phosphatases in forest soils were
higher than those in agriculture lands (Sakai and Tadano, 1993; Salam et al., 1997c;
1998d). Reddy et al. (1987) showed higher activities of several soil enzymes in the
rhizosphere soils than those in the non-rhizosphere soils. Rao et al. (1990) also
reported that rhizosphere soils showed higher activities than other soils: 26–158%
for acid phosphatase, 66–264% for alkaline phosphatase, and up to 292% for
dehydrogenase. Previously, Duxbury and Tate III (1981) showed that compared to
a fallow field, the activities of some soil enzymes were significantly enhanced by
grasses and sugarcane plants. Some reasearchers also found that the activities of
alkaline and acid phosphatases were higher in the root zones and decreased to the
directions of bulk soils uninhabited by plant roots (Joner and Jakobsen, 1995).
Salam et al. (1999e) also showed that the activities of enzymes were dependent on
types of plants and length of land cultivation.
Due to the influence of plant rootings, the activities of soil enzymes were
also reported to be soil-horizontal-distance and depth dependent. Joner and

Abdul Kadir Salam - 2014