Fungal communities and biomass in mountain streams affected by mine drainage tab: 3

Abstract

We examined fungi associated with decomposing leaves in streams to understand the effects of mine drainage on this community and to test a general model of ecological response to stress. The community composition and biomass of fungi and microbial activity associated with decomposing willow leaves were determined for 20 Colorado mountain stream sites, some of which were affected by mine drainage. The pH, concentration of dissolved zinc, and deposition rate of metal oxides were measured at each site. The community composition of fungi on willow leaves from litterbags was determined by analysis of conidia from aerated leaves and a particle-plating method. As with other communities in streams, diversity of fungal communities was sensitive to low pH and high concentrations of zinc from mine drainage, whereas biomass and functioning were stable under stress from pH or zinc. Diversity was low at sites with high concentrations of dissolved zinc (>1 mg/L) or low pH (<6). Fungal biomass (concentration of ergosterol) and microbial activity, in contrast, often were high despite the chemical conditions of the streams and the limited diversity of fungi. Microbial respiration was negatively related to the physical stress of metal oxide deposition. The concentration of ergosterol was significantly related to rates of respiration on leaves at pristine sites. Leaves from sites with high concentrations of dissolved zinc often had higher fungal biomass and microbial respiration than leaves from pristine sites. Several sites of low pH had high rates of respiration on leaves and visible fungal growth, but little or no measurable ergosterol. Leaves at these sites had ergosterol-like compounds that have yet to be identified.