DIATOM ECOLOGY IN THE PHYLLOSPHERE OF THE COMMON DUCKWEED (LEMNA-MINOR-L)

Epiphyton associated with thick, floating mats of the common duckweed (Lemna minor L.) was studied at four sites in western Canada between 1 985 and 1988. Maximum epiphyton abundance generally occurred in spring as biomass of the duckweed mat was increasing. Epiphytic biomass was low during summer and increased at some sites in autumn with mat decom position. The community was composed mostly of diatoms and, during sum mer, photosynthetic bacteria. Species richness of the diatom flora was low, suggesting that duckweed mats are environments to which few spec ies are adapted. Photosynthesis - irradiance curves indicated that duc kweed epiphyton was not adapted to low light levels that occurred in t he mat (< 1% of ambient), suggesting they may survive via other means of nutrition. The mat phyllosphere was also characterized by wide spat ial and temporal variation in temperature, and sharp vertical profiles of dissolved oxygen and nutrients.