[Effects of Hg contamination on paddy soil microbial and enzymatic activities]

With pot experiment, the microbial and enzymatic activities in two paddy soils were investigated at different Hg2+ loadings. The results showed that after harvest, all measured microbiological and enzymological indices including microbial biomass carbon, respiration rate, and activities of urease, acid phosphatase, and dehydrogenase in test soils were increased under low Hg treatments ( <2 mg Hg x kg(-1)) while decreased under high Hg treatments ( > or =2 mg Hg x 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 activity in test yellowish red soil was higher than that in test silty loam soil. ED50 analysis indicated that Hg had a stronger ecological toxicity on soil urease in test silty loam soil and on acid phosphatase in test yellowish red soil.