Survival of a Potamogeton pectinatus L. population under various light conditions in a shallow eutrophic lake (Lake Veluwe) in The Netherlands

Abstract

In Lake Veluwe, an eutrophicated shallow lake in The Netherlands, light connditions significantly affected the total biomass production of a Potamogeton pectinatus L. vegetation. A negative correlation was recorded between the annual biomass production and the mean daily photon flux densities in an experimental setup in which the photon flux densities were experimentally manipulated (four different levels of artificial shading) and the photoperiod was relatively unaffected. At the lowest mean photon flux density, the maximum total biomass was reached earlier in the growing season (end of June) than at the other photon flux densities (mid-August). Tuber production started at the same time in all conditions (mid-June). The numbers of tubers produced per gram ash-free dry weight of above-ground biomass was highest for the conditions with the lowest mean daily photon flux density. However, the total number of tubers per square metre recorded at the end of the growing season was highest for the control (no artificial shading). It is concluded that tuber initiation occurs under long-day conditions and is not controlled by mean daily photon flux densities. Tuber growth is clearly related to differences in daily photosynthetic periods. Tubers compete with above-ground biomass for photosynthate. At the highest level of shading, the photosynthetic tissue was ultimately unable to sustain tuber growth and, as a consequence, net growth of the vegetation ceased. Regarding tuber numbers of P. pectinatus in late summer, it is concluded that the size of the tuber bank was negatively affected by shade in the experiments.