Microfungi and microbial activity along a heavy metal gradient.

Soil fungal biomass, microfungal species composition, and soil respiration rate of conifer mor soil were studied along a steep copper and zinc gradient (up to 20,000 mug of Cu and 20,000 mug of Zn g dry soil) around a brass mill near the town of Gusum in South Sweden. Fungal biomass and soil respiration rate decreased by about 75% along the metal gradient. Above 1,000 mug of Cu g, the decrease was clearly evident; below 1,000 mug of Cu g, no obvious effects were observed, but there was a tendency for a decrease in total mycelial length. No decrease in CFU was found along the gradient, but fungal species composition was drastically changed. The frequency of the genera Penicillium and Oidiodendron decreased from about 30 and 20%, respectively, at the control sites to only a few percent close to the mill. Mortierella was most frequently isolated in moderately polluted sites, but at the highest pollution levels, a decrease in isolation frequency was evident. Some fungal taxa increased in abundance towards the mill, e.g., Geomyces (from 1 to 10%), Paecilomyces (0 to 10%), and sterile forms (from 10 to 20%). Analyses with a multivariate statistical method (partial least squares) showed that organic matter content and soil moisture had little influence on the fungal community compared with the heavy metal pollution.