Relation between the Distribution of Aquatic Hyphomycetes in Japanese Lakes and Lake Types

Abstract

Many excellent works on aquatic Hyphomycetes of freshwater lakes have been published in Europe and America during the past two decades. Among the contributions the writers recall the names of Ingold' 11), Ranzoni" 13), Nilsson14), Tubaki15) and othersl6, 17) These investigators, however, studied mainly the distribution and taxonomy of the fungi, and paid little attention to the ecology of them. The writers have engaged in floristic and ecological studies of the aquatic fungi for several years, emphasizing the relation of the distribution of aquatic Hyphomycetes and the physico-chemical properties of lake water. Experimental method The aquatic Hyphomycetes inhabits decaying leaves of trees fallen in lakes. Samples of these leaves were taken from lakes and those in stoppered bottles brought back into the laboratory. Six to ten leaves were collected from each lake. The collected materials were placed in petri dishes partially filled with autoclaved tap water. The specimens were allowed to stand at room temperature (15-25°) for 24 hours or more, then the conidia were found abundantly on the submerged leaves. The identification of species was carried out using a low power microscope. To make a detailed observation the fungus was stained with lactic phenol cotton blue. Distribution of aquatic Hyphomycetes The aquatic Hyphomycetes were widely distributed in the Japanese lakes. The distribution of the fungi, however, differed considerably with lake types (Table 1). On the basis of the qualitative data obtained, it is evident that the fungus flora was very rich in the harmonic lakes, while it was very poor in the dystrophic and acido-trophic lakes. In latter case, however, certain peculiar species adapting to the dis-harmonic water were found in large quantity. Although eleven species were isolated from the harmonic lakes, Tetrachaetum elegans, Articulospora tetraeladia, Lemonniera aquatica and Anguillospora longissima were the most prevalent in the lakes of this type. No aquatic Hyphomycetes, however , could be found in Lake Chuzenjiko and Towadako, which belong to the oligo-trophic type. On the other hand, aquatic Hyphomycetes were very slight or non-existent in the dystrophic lakes. As the lake water of this type contained large amounts of humic substances and reacted strongly acid, the physico-chemical specificities of the water may perhaps depress the activity of the fungi. Varicosporium elodeae seems to adapt to the dystrophic lakes. This species was found in neither the harmonic nor the acidotrophic lakes. It is a very interesting fact that Tricladium gracile var. oxyphilum and Anguillo