Abstract: Soil microorganisms were sensitive to heavy metal pollution, whose ecological effect on soil microbial community was impacted by the interaction of contaminated stresses and environmental factors. To explore the dominant factors governing those effects in heavy metal contaminated soil, field investigation was conducted for soil from different land use types in an area surrounding a typical mining smelter in Hunan Province. Soil microbial function parameters including microbial biomass carbon (MBC), basal respiration (BR), substrate-induced respiration (SIR) and nitrification potential (PNR) were used as measure endpoints for ecological effect to reflect soil carbon and nitrogen cycling. The results showed that the effect of land use on MBC, BR, and SIR was insignificant. The dominant impacting factors on microbial functions included CaCl₂ extracted Pb (CaCl₂-Pb) and soil organic matter (SOM) content. Results of multiple regression analysis showed that soil CaCl₂-Pb and SOM together explained 39.8%-58.3% of the total variations of BR, SIR and PNR in soil, when CaCl₂-Pb and SOM ranged in 0.004-13.14 mg·kg^-1 and 0.24%-4.34%, respectively. Significantly quantitative exposure-effect equations were developed between the responses of soil BR, SIR and PNR and soil CaCl₂-Pb and SOM when soil samples with medium contents (namely, SOM 1.70%～2.36% and CaCl₂-Pb 0.004-12.98 mg·kg^-1), which meant they could be used to quantitatively assess the ecological effect of heavy metals on microbial community function as measure endpoints.

Key words: mining smelter, microbial function, heavy metal, soil organic matter