Effects of Accumulation of Heavy Metals in Soils on Enzyme Activities
重金属积累对土壤酶活性的影响

Thirty-three soil samples were collected from farmland near a lead smelter in North China Plain, which were analyzed for the effect of accumulation of heavy metals in soils on the enzyme activities. The results indicated that average contents of the total Cd and Pb were 5.59 and 144 mg·kg-1, respectively. Average contents of DTPA-extractable Cd and Pb were 0.964 and 54.1 mg·kg-1, respectively. These values were higher than these in unpolluted Chao soil, while the total and DTPA-extractable contents of Cu, Ni and Zn were similar to the values of unpolluted Chao soil. Significant negative linear correlations were found between catalase activity and DTPA-extractable Pb, Cd and the total Pb (P<0.01). Compared with the activities of urease and phosphatase, the accumulation of heavy metals had a more serious effect on the activity of dehydrogenase. The activities of protease and phosphatase increased with increasing levels of DTPA-extractable Ni (P<0.1). No significant correlation was found between the urease activity and the total or DTPA-extractable contents of Cu, Zn, Ni, Pb and Cd (P>0.1). The results suggest that the activities of catalase and dehydrogenase in soil could be used to distinguish the degree of heavy metal pollution in soils with similar properties. DTPA-extractable heavy metals have a more profound effect than the total concentrations of heavy metals in soil on enzyme activities.