Multivariate analysis of microbial activity and soil organic matter at a forest site subjected to low-level heavy metal contamination

Soil respiration rate and a variety of soil characteristics including heavy metals, mineral content and organic matter quality were investigated at a forest site close to a former chloralkali factory. The data were analyzed using partial least squares regression (PLS). The respiration rate was most strongly correlated to contents of Ca, Mn, K and pH, while a smaller part of the variation could be explained by models using carbon fractionation data or heavy-metal contents. Hg and Pb concentrations, at average levels of 0.71 and 80 mg g-1dw, respectively, were negatively correlated to respiration rate. However, the heavy-metal contents were correlated to organic-matter quality in such a way that the correlation between respiration rate and heavy metals could not be attributed to a direct effect of the heavy metals on microbial respiration.