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

The nature of the relationships between host plants and associated microalgal epiphyton in freshwater ecosystems is largely undetermined. Many studies assume that the host plant, as a biologically active substrate, must have a direct influence on associated epiphytic communities, whereas other studies favor the view that host plants are a neutral substrate with only indirect effects on epiphytic communities. Here, we addressed the question of whether host plant taxonomic identity influences epiphyton community structure in 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 Sphagnum was found to support remarkably different epiphytic communities, probably including several microalgal substrate specialists. Other host plants we examined included Utricularia spp., Nymphaea spp., and Potamogeton natans L., 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, biomonitoring surveys should account for variation relating to this factor. Finally, our work showed that epiphytic diatoms (Bacillariophyceae) and desmids (Desmidiales) adopted similar group strategies, thus allowing for generalizations of patterns across entire microphytobentic communities.