Traditional microscope-based estimates of species richness of aquatic hyphomycetes depend upon the ability of the species in the community to sporulate. Molecular techniques which detect DNA from all stages of the life cycle could potentially circumvent the problems associated with traditional methods. Leaf disks from red maple, alder, linden, beech, and oak as well as birch wood sticks were submerged in a stream in southeastern Canada for 7, 14, and 28 days. Fungal biomass, estimated by the amount of ergosterol present, increased with time on all substrates. Alder, linden, and maple leaves were colonized earlier and accumulated the highest fungal biomass. Counts and identifications of released conidia suggested that fungal species richness increased, while community evenness decreased, with time (up to 11 species on day 28). Conidia of Articulospora tetracladia dominated. Modifications of two molecular methods-denaturing gradient gel electrophoresis (DGGE) and terminal restriction fragment length polymorphism (T-RFLP) analysis-suggested that both species richness and community evenness decreased with time. The dominant ribotype matched that of A. tetracladia. Species richness estimates based on DGGE were consistently higher than those based on T-RFLP analysis and exceeded those based on spore identification on days 7 and 14. Since traditional and molecular techniques assess different aspects of the fungal organism, both are essential for a balanced view of fungal succession on leaves decaying in streams.Aquatic hyphomycetes belong to a phylogenetically heterogeneous group of true fungi that dominate the breakdown of leaves and other allochthonous detritus in streams and rivers (5, 15). Their activity increases the palatability of the substrate to detritus feeders. Macroinvertebrates discriminate between, and show preferences for, particular fungal species (2, 6, 26). To fully characterize the fungal contribution to leaf decay and invertebrate nutrition, the aquatic hyphomycete community must be subdivided into its constituent species. The same principle applies when investigating relationships between biodiversity and ecological functions-a topic that has attracted increasing attention in the last decade (18,33).Most of the fungal biomass on decaying leaves consists of vegetative (nonreproducing) hyphae that cannot be identified through conventional microscopy. To characterize community structure, leaf surfaces often are examined for sporulating structures (e.g., see references 7 and 30), or conidia released from the leaf are collected, counted, and identified (e.g., see reference 3). The obvious shortcoming to these protocols is that absence of conidia might be due to the absence of species or to the presence of nonsporulating mycelium. In the initial phase of fungal colonization, between the landing of conidia and their growth into a sporulating colony, newly arrived species will escape detection by traditional microscope-based techniques.Molecular approaches characterize nucleic acids that are present in all...

Aquatic hyphomycetes are the main fungal decomposers of plant litter in streams. We compared the importance of substrate (three leaf species, wood) and season on fungal colonization. Substrates were exposed for 12 4-week periods. After recovery, mass loss, fungal biomass and release of conidia by aquatic hyphomycetes were measured. Fungal communities were characterized by counting and identifying released conidia and by extracting and amplifying fungal DNA (ITS2), which was subdivided into phylotypes by denaturing gradient gel electrophoresis (DGGE) and terminal-restriction fragment length polymorphism (T-RFLP). Mass loss, fungal biomass and reproduction were positively correlated with stream temperature. Conidial diversity was highest between May and September. Numbers of different phylotypes were more stable. Principal coordinate analyses (PCO) and canonical analyses of principal coordinates (CAP) of presence/absence data (DGGE bands, T-RFLP peaks and conidial species) showed a clear seasonal trend (Por=0.88). Season was also a significant factor when proportional similarities of conidial communities or relative intensities of DGGE bands were evaluated (P

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Virtual study models are clinically acceptable compared with plaster study models with regard to intrarater reliability and validity of selected linear measurements.

Freshwaters include some of the most impaired systems on Earth with high rates of species loss, underscoring the significance of investigating whether ecosystems with fewer species will be able to maintain ecological processes. The environmental context is expected to modulate the effects of declining diversity. We conducted microcosm experiments manipulating fungal inoculum diversity and zinc concentration to test the hypothesis that fungal diversity determines the susceptibility of leaf litter decomposition to Zn stress. Realized fungal diversity was estimated by counting released spores and by measuring species-specific biomasses via denaturing gradient gel electrophoresis. In the absence of Zn, positive diversity effects were found for leaf mass loss and fungal biomass through complementary interactions and due to the presence of key species. The variability of leaf decomposition decreased with increasing species number (portfolio effect), particularly under Zn stress. Results suggest that the effect of species loss on ecosystem stability may be exacerbated at higher stress levels.

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