Cellulase activity in forest humus along an industrial pollution gradient in Oulu, Northern Finland

Abstract

Decomposition of cellulose was studied in Scots pine stands lying on a sulphur and nitrogen concentration gradient from 1.3 to 2.8 g S kg −1 and from 7.9 to 16.3 g N kg −1 in mor humus. A number of biological variables had been found to decrease along the pollution gradient, e.g. soil respiration rate, microbial biomass, pine root mycorrhiza, diversity and sporophore production of mycorrhizal fungi, and the numbers of certain soil animals. Our aims were to evaluate two methods, cellulose decomposition determined in the field and cellulase activity determined in the laboratory, and to compare cellulase activity with other soil characteristics measured at the same sites. The activity of cellulase enzymes measured in the laboratory correlated well with basal respiration and correlated better with the S and N pollution gradient than the basal respiration rate. When cellulase activity was weighted toward the SIR values (substrate induced respiration), which reflect the amount of microbial biomass, it correlated best with the heavy metal concentrations in the soil especially in the most polluted stands. The decomposition of cellulose cardboard strips exposed in the field for 1 yr did not correlate with cellulase activity measured in the laboratory or with any pollution measurements, and this method seems to be too insensitive for measuring changes in microbial activities or the total decomposition process.