Effect of Submergence and Air Exposure of the Shoot on Growth, Nutrient Uptake and Photosynthesis in Monochoria vaginalis Presl.

Growth, nutrient uptake and photosynthesis as affected by submersion of shoot in pickerel weed (Monochoria vaginalis Presl.) were determined. The shoots of pickerel weeds in hydroponic culture were subjected to the submerged or emerged condition at 3- or 5-leaf stage for 8 or 10 days. Under submerged condition, growth in plant height was enhanced, but leaf number, leaf area, fresh and dry weight were reduced compared to those under the emerged condition. Similar responses in growth to submergence were obtained with the pickerel weeds rooted in the soil. Under submergence, chlorophyll content increased during the first 2 days, but thereafter remarkably decreased at 3-leaf stage and after the first 4 days at 5-leaf stage. Compared to the emerged condition, uptakes of -N, -N, and were reduced, but uptakes of and increased under the submerged condition. Photosynthetic rate of shoot under water, measured by electrode, showed the maximum by 210 moles /g F.W. at the 8th day after submergence(DAS) at 3-leaf stage and 320 moles /g F. W. at 6 DAS at 5-leaf stage. These results indicate that pickerel weeds grow much better when the shoot is air-exposed and are less tolerable to submergence at 3 leaf-stage than at 5-leaf stage.