INFLUENCE OF PROPAGULE SIZE, SOIL FERTILITY, AND PHOTOPERIOD ON GROWTH AND PROPAGULE PRODUCTION BY 3 SPECIES OF SUBMERSED MACROPHYTES

Potamogeton pectinatus, P. gramineus, and monoecious Hydrilla verticil lata were grown in greenhouse experiments at 2 photoperiods, 5 levels of sediment nutrients, and from initial propagules of 3 different size classes to determine how these factors influenced growth and producti on of vegetative propagules. Potamogeton pectinatus weight increased w ith increasing tuber size and soil fertility, but differences between plants grown at two photoperiods were small. Mean weight of tubers was greater for plants grown under a 10-h photoperiod and from tubers in the medium or large size class. Tuber production by plants grown from small tubers under a 10-h photoperiod was much less and was about the same as that for all plants grown under the 16-h photoperiod whatever the initial tuber size. Potamogeton gramineus weight was greater for p lants grown on more fertile soils at the 16-h photoperiod. Plant weigh ts at the 10-h photoperiod were less affected by soil fertility. Plant s from larger winter buds weighed more. Winter buds were only produced under the 10-h photoperiod. For H. verticillata, there were several s ignificant interactions. In general, plants from larger tubers weighed more if they grew on more fertile soils or at the 16-h photoperiod. P lants grown at the short photoperiod produced more tubers with increas ing soil fertility and with increasing propagule size. These results i mply that propagule size may be important in determining aquatic plant persistence in an area through its effects on growth and propagule pr oduction.