Abstract: With pot experiment, the microbial and enzymatic activities in two paddy soils w ere investigated at different Hg2+ loadings. The results showed that a fter harvest, all measured microbiological and enzymological indices including m icrobial biomass carbon, respiration rate, and activities of urease, acid phosph atase, and dehydrogenase in test soils were increased under low Hg treatments (< 2 mg Hg·kg-1) while decreased under high Hg treatments (≥2 mg Hg·kg -1), except the basal respiration and metabolic quotient were partly increased with increasing Hg level. Among the test indices, soil microbial quotient was a microbiological index more sensitive to Hg contamination. The enzymatic activit y in test yellowish red soil was higher than that in test silty loam soil. ED 50 analysis indicated that Hg had a stronger ecological toxicity on soil ure ase in test silty loam soil and on acid phosphatase in test yellowish red soil.

Key words: vegetation dynamics, human activity, ecological project.