Page 51 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 39

Jakobsen (1995) reported that the activities of acid and alkaline phosphatases at
10 – 20 cm were lower than those at 0 – 10 cm away from cucumber roots. Some
researchers also showed that topsoils were also shown to have higher activities of
soil enzymes than did subsoils, partially due to the presence of plant roots
(Duxbury and Tate III, 1981; Salam et al., 1998d; 1999d). Naseby and Lynch (1997)
found that the microbial biomass and measured enzyme activities of alkaline
phosphatase, phosphodiesterase, arylsulfatase, and urease decreased with soil
depth. However, a close relationship between topsoil and subsoil enzymatic
activities (Salam et al., 1998d; 1999d; Salam et al., 2001) may to some extent
indicate that enzymes are produced in topsoil but may be partially leached through
the soil profiles by percolating water to subsoils. The relationship between the
activity of phosphomonoesterase and soil depth is depicted in Fig. 4.4.

20

16

Activity (EU 10 -3 ) 12 Acid

Phosphatase
8
Alkaline
4 Phosphatase

0
0 4 9 14 19 24
Distance from Roots (mm)

Fig. 4.3. The average activities of acid and alkaline phosphatases
close to the plant root surface of cucumber
(Drawn from Joner et al., 1995).

4.2 Forms of Soil Enzymes

Soil enzymes are found in various chemical forms. According to Sarkar et al.
(1989) and Tabatabai and Fu (1992), a part of soil enzymes is soluble in soil water

Abdul Kadir Salam - 2014