Fungi in the hyporheic zone of a springbrook.

Eight bimonthly sediment core samples (n = 6) were collected, to a depth of 64 cm, from the hyporheic zone of a springbrook in southern Ontario, Canada. Sediment cores were divided into three to four sections, and organic matter was subdivided into six different categories. Twigs were the most common substrate, followed by roots, cedar leaves, wood, grass, and deciduous leaves. The contributions of deciduous and cedar leaves declined with depth, whereas that of wood increased. On each sampling date and from each section, three randomly chosen substrates >3 cm were examined for conidia of aquatic hyphomycetes. The number of identified species significantly decreased with depth, and was highest on deciduous leaves and lowest on wood. Season had no significant effect on species numbers. DNA from substrates was extracted, amplified with fungal primers, and differentiated into phylotypes with denaturing gradient gel electrophoresis (DGGE). Absence/presence patterns of phylotype were significantly affected by season but not by section level. Both season and section level significantly affected relative densities of the bands of the 10 most common phylotypes. Our data suggest that aquatic hyphomycetes and other fungi readily disperse within the hyporheic zone, and that their relative scarcity in this habitat is due to a lack of suitable substrates.

Diversity of conidia of aquatic hyphomycetes assessed by microscopy and by DGGE.

Water samples from a Canadian stream were passed through membrane filters between 22 July 2002 and 19 May 2003. Filters with trapped conidia of aquatic hyphomycetes were cut in half. One half was examined under a light microscope, and conidia were counted and identified. From the second half, DNA was extracted and amplified with fungal primers. The number of different ITS sequences (phylotypes) in the amplified DNA was assessed with DGGE. On average, the number of visually identified species per sample (12.4) was higher than the number of phylotypes (11.7), but the difference was nonsignificant (P = 0.36). However, the difference between species and phylotype numbers increased significantly with the number of species or conidia present on the filter, indicating that the sensitivity of DGGE decreases with sample size. When few conidia were present, phylotype numbers often exceeded species numbers, suggesting insufficient resolution of visual identification or the presence of DNA from nonconidial sources. A modification of the described method may be useful to check the accuracy of taxonomy and identification based on conidial morphology.