Asexual reproduction for overwintering of the submersed macrophyte Vallisneria spinulosa at different light intensities

The dynamics of plant populations are highly influenced by light-dependent growth features and patterns of reproduction when overwintering. Vallisneria spinulosa is a common submersed macrophyte and has been widely used in lake restoration projects. The relationship between reproduction when overwintering and regrowth in the following year is not well known and may vary with light intensity. In this study, reproduction and plant growth of V. spinulosa were tested at three light intensities (high, moderate and low, i.e. 50%, 15% and 7% of full sunlight, respectively) for 1 year. Asexual reproduction by forming winter tubers in the sediment was found to be of greater significance for population maintenance than sexual reproduction. Plant biomass and ramet number remained unchanged between October and June in the following year at both 15% and 7% of full sunlight, suggesting that the light requirement for population maintenance is low. At high light, plant biomass, ramet number and tuber biomass were higher and plants tended to form a larger number of small-sized than large-sized tubers. Small-sized tubers featured a high nitrogen content and germinated early, while large-sized tubers were characterised by a high carbon content and germinated later in spring. Thus, there probably is a trade-off between the germination schedule and carbon and nitrogen contents, depending on tuber size. Large numbers, high nitrogen content and early germination of small tubers at high light supported fast establishment of V. spinulosa populations in spring. Our study highlights the importance of asexual reproduction as contributing to a high competition and expansion capacity for V. spinulosa populations, making it a valuable species to focus on for lake management and restoration.