Flowering, Germination and Zonation of the Submerged Aquatic Plant Lobelia Dortmanna L.

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Abstract
(1) Lobelia dortmanna L. was studied in some Scottish lochs. It flowered from May to October. The number of flowers per plant was greater in less exposed sites. Larger plants were more likely to flower and small plants did not flower. Plants flowered to the depth limit in one loch, producing totally submerged flowers. These results are discussed with reference to current hypotheses of resource allocation. (2) Almost all capsules set seeds, most of which were viable (including those of submerged flowers). Seeds sank quickly and become buried up to 10-mm deep in the loch sediment. A cold-stratification period was found to be necessary before germination and seeds could survive both drying and freezing. Germination could proceed over a 15.degree.-25.degree.C temperature range, though below 20.degree. C rats were low. The seeds required light for germination, with some evidence of red promotion and far-red inhibition. Germination could also take place at very low light levels (PAR=4 .mu.mol photons m-2s-1). Anoxia induced a secondary dormancy that required further cold-stratification to break it. (3) Seedlings in culture were unable to survive at the low light intensities that permitted germination. (4) In the lochs, sufficient light was available to allow germination well below the observed zonation limits of L. dortmanna. Light was rapidly absorbed by the sediment so some buried seeds would be unable to germinate. (5) The vertical zonation of this species is not controlled by seed germination requirements, but by the inability of plants to grow at the low light levels in deeper water.