[Changes of soil enzyme activities in heavy metals polluted region: a case study in a wastewater-irrigated agricultural area near a smelter in Xinluo District of Longyan City, Fujian Province].

Surface soil samples were collected from a wastewater-irrigated agricultural area near a smelter in the Xinluo District of Longyan City, Pujian Province, and their basic physical and chemical properties, activities of urease, cellulase, alkaline phosphomonoesterase, polyphenol oxidase and catalase, and contents of Cu, Cd, Pb and Zn were determined, aimed to approach the effects of heavy metals pollution and soil properties on the activities of soil enzymes. Correlation analysis showed that the total and available contents of soil Cu, Cd, Pb and Zn had significant positive correlations with the activities of soil urease, cellulase, alkaline phosphomonoesterase and polyphenol oxidase, but significant negative correlation with the activity of soil catalase. Soil pH had significant positive correlation with the activity of soil alkaline phosphomonoesterase, and soil silt content had significant negative correlation with the activity of soil catalase. Path analysis showed that Cu, Cd, Pb and Zn pollution promoted the activities of soil urease, cellulase and polyphenol oxidase, but had less effects on the activity of soil alkaline phosphomonoesterase. Soil available Cu, Cd, Pb and Zn didn't directly affect the activity of soil catalase, but indirectly inhibited it significantly. Soil physical and chemical properties had greater effects on soil enzyme activities, e.g., alkaline-hydrolyzable N directly inhibited the activity of soil urease, total P directly stimulated the activities of soil alkaline phosphomonoesterase and catalase and indirectly stimulated the activity of soil cellulase via available P, available P directly promoted the activity of soil cellulase but inhibited the activities of soil alkaline phosphomonoesterase and catalase, total K directly inhibited the activities of soil alkaline phosphomonoesterase and polyphenol oxidase, available K stimulated the activity of soil catalase via available P, and particle composition had significant effects on the activities of soil polyphenol oxidase and catalase. The above results demonstrated that because of the complicated and uncertain relationships between the contents of soil Cd, Pb, Zn and Cu and the activities of the five soil enzymes, it should be cautious to use the test enzyme activities to indicate soil heavy metals pollution.