2009 Volume 3 Issue 2 Pages 172-182
The aim of this research was to observe differences in beta-glucosidase activity and changes in the community structure of soil microbes in chemically and organically fertilized soils. Beta-glucosidase is one of the most important enzymes produced by soil microbes because it plays a key role in the decomposition of cellulose debris added to soil as fertilizer. A soil rich in bacterial diversity is stable and suitable for optimal plant growth. Soils with very low nitrogen and carbon content were examined under natural weather conditions in Japan. Significant differences (P<0.05) were observed in beta-glucosidase activity between the different treatments as measured by colorimetric analysis. Beta-glucosidase activity increased in all pots but at different rates. After 60 days, composted manure (treatment 1) and the combination of chemical and fertilizers and composted manure (treatment 3) showed the highest and second highest levels of beta-glucosidase activity, respectively. Treatment 1 showed 30% higher beta-glucosidase activity as compared to treatment 3 and 75% higher beta-glucosidase activity as compared to treatments 2 and 4 (control).
The community structure of the soil bacteria was assayed by the PCR-denaturing gradient gel electrophoresis (PCR-DGGE) technique. We captured the banding pattern of soil microbes on the gel images following DGGE of PCR-amplified 16S rDNA using the 357F and 518R primers. Although the gross trend was the same, the four different treatments showed differences in the DNA banding pattern, suggesting differences in the soil bacterial species community structure among the four different soil treatments. Treatment with chemical fertilizers gave a few intense bands, whereas treatment with composted manure and treatment with a combination of chemical fertilizer and composted manure yielded more bands that were less intense. These findings suggest that chemical fertilizers promote the colonization of specific dominant bacterial species, whereas composted manure promotes diversity in the soil bacterial population. Principal component analysis confirmed that the treatment 1, 2 and 3 results varied markedly from the treatment 4, control results. We conclude that exclusive use of chemical fertilizers in soils with low or moderate carbon levels would lead to low beta-glucosidase activity and a reduction in the diversity of the soil microbe community structure. Low beta-glucosidase activity and reduced soil bacterial diversity might be detrimental to the condition of the soil and lead to an increase in the soil's postharvest recovery period and a reduction in the preseason decomposition rate of plant residues in the soil.
