Field and greenhouse investigations on winter bud production by Potamogeton gramineus L

Potamogeton gramineus L. winter buds were present in the Byrnes Canal in northern California from August through October. Density (number m −2) of winter buds increased during this period and was inversely related to photoperiod. Density varied from year to year (1985–1991) and maximum average density of 761 m −2 was recorded in 1986. In greenhouse experiments, winter buds were present on plants after 8–10 weeks of growth at a 10 h photoperiod, but not at a 14 photoperiod. Plants grown at a 10 h photoperiod but with the dark period interrupted with either 20 or 60 min of dim light at 13 μM m −2 s −1 did not produce winter buds. Similar plants grown at a 10 h photoperiod with no interruption of the dark period produced winter buds. Plants grown with interruption of the dark period displayed dry matter allocation patterns similar to plants grown at a 16 h photoperiod. This information confirms earlier reports with other species about the importance of photoperiod for initiating vegetative propagule formation, and will improve capabilities for predicting vegetative reproduction by rooted aquatic plants.