CHAPTER 15 – Fungi: Biomass, Production, and Sporulation of Aquatic Hyphomycetes

Fungi are common inhabitants of stream ecosystems. All phyla of true fungi (Chytridiomycota, Zygomycota, Ascomycota, and Basidiomycota) and also the Oomycota (kingdom Stramenopila) that are morphologically similar to fungi can be observed in or isolated from stream environments. The most ecologically important and well studied fungi in streams are the “aquatic hyphomycetes,” which are anamorphs (asexual stages) of ascomycetes or basidiomycetes. These fungi are capable of completing their entire asexual life cycle underwater starting from colonization of suitable substrate followed by intramatrical mycelial growth and abundant sporulation. Up to 80% of fungal production may be invested into conidia (i.e., asexual spores) (Suberkropp 1991). Conidia of aquatic hyphomycetes are often tetraradiate, variously branched, or filiform (rarely conventionally shaped) (Figure 15.1), which is an adaptation to dispersal in flowing water and enhances the probability of attachment to fresh substrates (Webster and Descals 1981). Allochthonous organic matter (leaves of deciduous trees, twigs, etc.) is an important source of energy and nutrients in small forest streams (Fisher and Likens 1973, Kaushik and Hynes 1968) and fungi are the main colonizers of this plant litter. Maximum fungal biomass and sporulation rate of aquatic hyphomycetes correlate well with plant litter breakdown rate (Gessner and Chauvet 1994, Niyogi et al. 2003), suggesting that fungi are

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