中沼における水生菌類の季節的変化

抄録

1. The seasonal variations of aquatic Phycomycetes were studied from October 1957 to September 1958 in Lake Nakanuma, Ibaraki Prefecture, Japan. The thermal stratification was established from May to December. 2. The number of the zoospore of aquatic Phycomycetes varied considerably through the year with one maximum and one minimum. The maximum appeared in early winter and the minimum in summer. The zoospore was counted 65/10cc and 0/10cc respectively. 3. The aquatic Phycomycetes consisted of seven species, in which Pythium sp. was the dominant one. The seasonal changes differed with each species. Saprolegnia monoica, S. ferax, Achlya flagellata and Dictyuchus sp. were found mostly in winter. Aphanomyces sp. and Pythium sp., however, were seen through the year with the maximum in winter. 4. There were two main types in the vertical distribution of the zoospore of aquatic Phycomycetes. The one was homogeneous distribution and the other was the stratum one. The former appeared during the circulation period and the latter was seen during the stagnation period. 5. The zoospore production of aquatic Phycomycetes was effected by the water temperature as well as by the lacustrine bacteria. The optimum temperature for the zoospore formation differed in each species.