Page 48 - Enzymes in Tropical Soils

36 Enzymes In Tropical Soils

Since the experiment was conducted in the absence of plant roots and soil
macroorganisms (earthworms), the increase in soil phosphatase activity was
concluded to be attributed to the presence of soil microorganisms. The presence
of water until 40% (about the soil field water capacity) may have increased the
populations and activities of soil microorganisms and, hence, increased the
production of soil enzymes. Of course, to some extent the presence of water may
have also dissolved part of the adsorbed soil enzymes previously inactive.
The activity of phospahatase, however, decreased with the increase in water
contents above 40%. After 40%, water filled more soil pores and , hence, limited
the O 2 diffusion needed for respiration by microorganisms. The energy obtained by
soil microorganisms then somehow became more limited. Consequently, as shown
in Fig. 4.1, the activity was lower at water contents higher than 40%. Some other
workers (Klein and Koths, 1980; Tabatabai, 1982; Baligar et al., 1988; Yusnaini et
al., 2002) also reported that the presence of water increased the activity of soil
enzymes.
The finding of Yusnaini et al. (2007) also suggests that the soil
microorganisms were the producers of enzymes in soils. They showed an
increasing pattern in CO 2 evolution due to the addition of green and chicken
manures as shown in Table 5.4 in the following Chapter V. The pattern was similar
to the increase in the activities of alkaline phosphatase and -glucosidase as green
manure or chicken manure was enhanced, shown in Table 5.13 in the following
Chapter V. 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.
A study by Frankenberger and Dick (1983) also showed that alkaline
phosphatase, amidase, -glucosidase, and dehydrogenase activities were
significantly related to the microbial respiration as measured by CO 2 evolution.
Alkaline phosphatase, amidase, and catalase were correlated with the microbial
respiration and total biomass in soils, indicating the role of soil microorganisms in
producing enzymes. The relationship between the activities of alkaline
phosphatase and -glucosidase is given in Fig. 4.2. Dharmakeerti and Thenabadu
(1996) also stated that urease in soils is mainly of microbial origin. Klose et al.
(1999) found that about 45% of the total arylsulfatase activity in soils was
extracellular and the rest 55% was associated with the microbial biomass in soils.
These facts indicate the importance of the microflora as an enzyme source in soils.
Tarafdar and Marschner (1994) reported the role of fungi in producing soil
enzymes. They observed that the activity of acid phosphatase was higher than that
of alkaline phosphatase and both were slightly enhanced by mycorrhizal infection.

Abdul Kadir Salam - 2014