Host specificity of epiphytic diatom (Bacillariophyceae) and desmid (Desmidiales) communities

The nature of the relationships between host plants and associated microalgal epiphyton in freshwater ecosystemsis largely undetermined. Many studies assume that the host plant, as a biologically active substrate, must have a direct influence on associated epiphyticcommunities, whereas other studies favor the view that host plants are a neutral substrate with only indirect effects on epiphyticcommunities. Here, we addressed the question of whether host plant taxonomic identity influences epiphyton community structurein comparison with other factors (which also provided further insight into the general ecology of freshwater microphytobenthos) by examining four types of natural plant substrates at five freshwater sites in the Czech Republic. The results demonstrated that host plant type significantly affected epiphytic community structure; most notably, the genus Sphagnumwas found to support remarkably different epiphyticcommunities, probably including several microalgal substrate specialists. Other host plants we examined included Utriculariaspp., Nymphaeaspp., and Potamogeton natansL., all of which were presumably neutral substrates. The differences among the host plants varied among sites, however, suggesting the presence of an interaction between these two factors. Thus, we concluded that host plants may not always provide a neutral substrate for microalgal epiphyton and, consequently, biomonitoringsurveys should account for variation relating to this factor. Finally, our work showed that epiphyticdiatoms (Bacillariophyceae) and desmids ( Desmidiales) adopted similar group strategies, thus allowing for generalizations of patterns across entire microphytobentic communities.