Emergence of vegetative propagules of Potamogeton nodosus, Potamogeton pectinatus, Vallisneria americana, and Hydrilla verticillata based on accumulated degree-days

The purpose of this study was to develop equations that predict emergence f rom vegetative propagules for four species of aquatic plants. We establishe d artificial propagule banks by growing monoecious and dioecious Hydrilla v erticillata (L.f.) Royle, Potamogeton pectinatus L., Potamogeton nodosus Po iret in outdoor tanks in Davis, California. Dioecious H. verticillata, P. p ectinatus, P. nodosus and Vallisneria americana L. were grown in similar ta nks in Lewisville, Texas. Emergence of undisturbed propagules was monitored the following spring. In California, P. pectinatus tubers, P. nodosus wint er buds, and axillary turions formed by monoecious H. verticillata began to sprout at about the same time in mid-February, while dioecious H. verticil lata tubers did not begin to emerge until mid-August. The distinct separati ons of emergence times for propagules in the Texas experiment were similar to those observed in California, and V. americana showed the earliest emerg ence time. Using sediment temperature data from each location, we calculate d degree-days using the single triangle method. We fit a single logistic eq uation relating cumulative emergence to accumulated degree-days for each sp ecies-propagule combination from the two locations. (C) 2000 Elsevier Scien ce B.V. All rights reserved.