Changes in epilithic fungal communities under different light conditions in a river: A field experimental study

In lotic ecosystems, the community structure of periphytic fungi changes depending on the quantity and quality of allochthonous organic matter supplied. However, little is known about the effects of the input of autochthonous organic matter on the community structure. To examine the relationship between a periphytic fungal community grown on inorganic substrates and the algal production, we performed field experiments. If the fungal species differ in their relative ability to exploit allochthonous and autochthonous organic matter, the species composition of the fungal community might differ between shaded conditions, without algal production, and light conditions, with algal production. To examine such a possibility, we assessed the fungal community that developed on ceramic tiles that were fixed on opaque or clear pipes at three sites in the Natori River. The experiment showed that the periphytic chlorophyll a and the number of fungal species in the unshaded tiles were significantly greater than those in the shaded tiles. However, a nested structure was not detected between the fungal assemblages of the unshaded and shaded tiles. Instead, the taxon compositions largely differed between these tiles, which indicated most fungal species that colonized the shaded condition were replaced by others in the unshaded condition where algae grew. The results indicate that light facilitate the colonization and growth of several epilithic fungal species through the growth of sessile algae and suggest that not only the supply of autochthonous organic matter but also biological interactions play a pivotal role in shaping the epilithic fungal communities in lotic habitats.