ABSTRACT
If heavy metals reduce the efficacy of fungal hyphal activity, it is reasonable to assume that the ecosystem-level functions carried out by fungi will be impacted. In terms of the role of fungi in decomposition and nutrient mineralization, Bardgett et al. (1994) investigated the effects of chromium, copper, and arsenic wood preservatives on soil microbial and nematode communities. They found that increasing levels of each preservative had little effect on the biomass of the prokaryotic microbial community but a significant negative effect on the eukaryotic (presumed fungal) biomass as measured by substrate-induced respiration. This suggests that fungi are more sensitive to heavy metals than bacteria. Indeed, although Jordan and Lechevalier (1975), and Nordgren et al. (1986) found the reverse to be true, they showed that the decomposition of cotton strips (cellulose) was significantly reduced at higher heavy metal concentrations. As cellulose decomposition in soil is mainly effected by fungi, it is probable that heavy metals had an effect on fungal metabolism, if not on biomass. Kuperman and Carreiro (1997), however, showed that total and fluorescein diacetate active (FDA) fungal biomass and enzyme activity was reduced in heavy metal-contaminated (As, Cd, Cr, Cu, Ni, Pb, and Zn) soils of the Aberdeen Proving Grounds in Maryland. The presence of heavy metals reduced the activity of the enzymes N-acetylglucosaminease, β-glucosaminease, endocellulase, and acid and alkaline phosphatase by ten-to 50-fold. Nitrogen mineralization by both fungi and bacteria has been shown to be reduced by the presence of heavy metals in forests soils (Necker and Kunze, 1986) because of the maintenance of high levels of soluble Zn, Cd, and Ni in acidic soils. Lead, on the other hand, was the only metal to be less available under these soil-acidifying conditions, because of its being complexed onto humic materials in soil and thus becoming less available to other organisms.
