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 from vegetative propagules for four species of aquatic plants. We established artificial propagule banks by growing monoecious and dioecious Hydrilla verticillata (L.f.) Royle, Potamogeton pectinatus L., Potamogeton nodosus Poiret in outdoor tanks in Davis, California. Dioecious H. verticillata, P. pectinatus, P. nodosus and Vallisneria americana L. were grown in similar tanks in Lewisville, Texas. Emergence of undisturbed propagules was monitored the following spring. In California, P. pectinatus tubers, P. nodosus winter buds, and axillary turions formed by monoecious H. verticillata began to sprout at about the same time in mid-February, while dioecious H. verticillata tubers did not begin to emerge until mid-August. The distinct separations of emergence times for propagules in the Texas experiment were similar to those observed in California, and V. americana showed the earliest emergence time. Using sediment temperature data from each location, we calculated degree-days using the single triangle method. We fit a single logistic equation relating cumulative emergence to accumulated degree-days for each species-propagule combination from the two locations. (C) 2000 Elsevier Science B.V. All rights reserved.