Effects of whole-stream nutrient enrichment on the concentration and abundance of aquatic hyphomycete conidia in transport

Abstract

The concentrations and relative abundances of aquatic hyphomycete conidia in water were followed during a three-year study in two headwater streams at Coweeta Hydrologic Laboratory, North Carolina, using the membrane-filtration technique. After a one-year pretreatment period, one of the streams was enriched continuously with inorganic nutrients (N+P) for two years while the other stream served as the reference. This ecosystem-level nutrient manipulation resulted in concentrations of aquatic hyphomycete conidia in the water of the treated stream that were 4.5–6.9 times higher than the concentrations observed during the pretreatment period and in the reference stream. Nutrient enrichment led to an increase in the number of fungal species detected on each sampling date. Changes in dominance patterns and relative abundances of individual species also were detected after treatment. Nutrient addition stimulates the reproductive activity of aquatic hyphomycetes, their colonization success and fungal-mediated leaf-litter decomposition. Such changes in the activity of the fungal community might affect higher trophic levels in lotic ecosystems.

• community structure
• freshwater fungi
• nitrogen
• phosphorus
• seasonal pattern

We are grateful to H. Weyers for help with sample collection and J. Benstead for providing long-term nutrient data for both streams. This work was supported in part under NSF-NATO Postdoctoral Fellowship in Science and Engineering awarded to VG and by NSF grant DEB 9806610.