Page 148 - Enzymes in Tropical Soils

136 Enzymes In Tropical Soils

Reddy and Faza (1989) also mentioned that the decrease in dehydrogenase
activity in sludge-amended soil could be due to the heavy metals concentration in
sewage sludge. Tate III (1987) reported that organic molecules, like soil enzymes,
may strongly complex heavy metals. This association may lower the capacity of soil
enzymes in catalyzing the the biochemical decomposition of organic matters. Dick
and Tabatabai (1983) previously reported that at particular concentrations Ba(II),
Ca(II), Co(II), Mg(II), Ni(II), and Zn(II) promoted while Fe (II) and Cu(II) decreased
the soil pyrophosphate activity.

1.2
Soil 1: Pb
1
Soil 1: Cd
Relative Activity 0.8 Soil 2: Pb

Soil 2: Cd
0.6

0.4
0.2
0 2.5 5 10 15 20 30 40
-1
Heavy Metal Addition (mg kg )

Fig. 9.4. The effect of Pb and Cd on soil phosphatase activity
(Adapted from Salam et al., 1997f).

Park et al. (1992) observed differences in the effects of heavy metal Zn and
major cations Ca and Mg on the soil enzymatic activities (Fig. 9.5). The activities of
phosphomonoesterase and phosphodiesterase from Lumbriscus terrestris were
strongly inhibited by the presence of Zn. However, Ca was shown to stimulate the
activities of phosphomonoesterase and phosphodiesterase; while Mg did not give a
significant effect. The activity of acid phosphatase was reported to not decrease
2+
2+
+
2+
significantly by high concentrations of K , Mg , Zn , and Cu in the range

Abdul Kadir Salam - 2014