Germination and early growth of Nymphaea odorata at different water depths

We experimentally determined the effects of water depth on seed germination and seedling growth and morphology, and we documented the transition from submerged to emergent plants in the white water lily, Nymphaea odorata. Seeds of N. odorata were germinated at 30, 60, and 90 cm water depth in outdoor mesocosms and percent germination and morphology measured after a month. The presence of self-seeded seedlings in pots at the same 3 water levels was also recorded over two years. To examine juvenile growth, seeds planted in soil were placed at the same mesocosm depths; germination and growth were monitored for three months, when the plants were harvested for morphological and biomass measurements. N. odorata germinated equally well in 30, 60 and 90 cm water; seedlings grew as submerged aquatics. After one month, seedlings in 90 cm water had less biomass than those in 30 cm (1.1 vs. 3.3 mg and 1.0 vs. 1.8 mg for different seed sources, respectively) and allocated relatively more biomass to shoots (97.5 vs. 67.8% and 73.1 vs. 58.0%, respectively). Seedlings in 60 cm water were intermediate. After 3 months of submerged growth, plant biomass remained less in 90 vs. 60 and 30 cm water (22.5 vs. 36.4 and 33.3 mg, respectively). Plants in 90 and 60 cm water had greater biomass allocation to shoots than plants in 30 cm water (85.7 and 72.6% vs. 64.4%, respectively) and produced larger laminae on longer petioles (lamina length = 33.3 vs. 25.2 mm in 90 vs. 30 cm; petiole length = 99.0 vs. 36.0 mm, respectively). After about 3 months, submerged plants produced floating leaves that had 39% shorter laminae but 267% to 1988% longer petioles than submerged leaves on the same plant. Lamina length to width allometric relations of submerged leaves were >1 at all water levels, distinguishing them from the equal allometry of adult floating leaves. The switch from production of submerged to emergent leaves resembles submergence-escape growth in other aquatics, but because the seedlings have been submerged throughout their life, submergence itself cannot be the stimulus to produce emergent leaves in these totally immersed plants. Our data show that N. odorata plants can establish from seeds in up to 90 cm water and that seedlings grow as submerged aquatics until they switch abruptly to production of floating leaves.