Overwintering and re-emergence in Lemna minor

Abstract

In cold climates, aquatic plants employ a variety of strategies to survive winter, usually by either going to seed, or by producing resistant vegetative tissue that can withstand freezing. Although Lemna minor, the common duckweed, reproduces almost exclusively by asexual vegetative propagation and lacks any additional specific overwintering structure, it thrives over a vast geographic distribution including in northern climates. It is often thought that populations are subjected to a seasonal bottleneck with only a small proportion of plants surviving to found the following year’s population. In this study we use experimental enclosures to measure re-emergence of L. minor in a forested pond in Quebec, Canada, after four months of ice cover. Frond recruitment as surface re-emergence and relative growth rate were estimated and compared to the pre-winter population. To our surprise, 92% of fronds survived the winter, indicating the virtual absence of any bottleneck. Lemna minor is then essentially perennial, which despite having a life span of just a few weeks in favourable conditions, can easily endure several months under surface ice cover.