抄録
Duckweeds (Lemna paucicostata Hegelm.) grow all over the world as a weed in paddies or ponds. They grow under the low light intensity. So, turbulent fluxes of carbon dioxide and water vapor within rice plant canopies are influenced by physiological activities of duckweeds. Although studies on leaf gas exchanges of duckweed are important, continuous measurements have been seldom made. Therefore, an open measurement system for photosynthesis was assembled. The observations were made under natural light conditions.
The net photosynthesis rates of duckweed began to rise rapidly after the sunrise and became maximum at 10 o’clock. They were almost constant in the daytime and then decreased in the evening. Net photosynthesis fell into negative ranges in the evening and reached to minimum after sunset. For respiration rates, there was a tendency to decrease from the night to dawn.
Photosynthesis rates of duckweed linearly increased to 4.2μmolCO2m-2s-1 as light intensity increased to 600μmol m-2s-1PAR where plants were light saturated. The light compensation point was less than 60μmolm-2s-1PAR. The light responses curve was well approximated by the non-rectangular hyperbola.
These results show that this measurement system will become a useful method to study diurnal variations of leaf gas exchanges of duckweed.
