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The periphyton of Nuphar lutea (L.) Sm. and Nymphaea alba L., the dominating species of the vegetation of an old branch of the River Waal near Nijmegen, was studied from May until October 1981. The study evaluated the influence of the architecture of nymphaeid plants on the periphyton-composition of different plant parts. In particular the composition of the epiphytic diatom-flora was studied. The first part of this study consisted of analyses of the diatoms present on the underside of healthy looking floating leaves of both species. For this purpose, leaves with a distinct visible horizontal zonation were collected. Although light could be expected to be an important factor affecting the distribution of diatoms on the underside of floating leaves, the results of the analyses indicated that the period, during which the particular leaf-area becomes exposed to be surrounding water, is most important. The spatial differences in the studied area were not determined by their position but they reflect the differences in time of colonization, which are sufficient to explain the differences in the various diatom populations. Differences in the diatom flora between the floating leaves of the two nymphaeid species could not be detected. |
