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Photorespiration and internal recycling of CO 2 in the submersed angiosperm Scirpus subterminalis

1980; Canadian Science Publishing; Volume: 58; Issue: 6 Linguagem: Inglês

10.1139/b80-075

1480-3305

Martin Søndergaard, Robert G. Wetzel,

Plant responses to water stress

The presence and magnitude of photorespiration in the submersed freshwater angiosperm Scirpus subterminalis Torr. was investigated by gas-exchange characteristics in an open water-flow system. The minimal rates of photorespiration during active photosynthesis were measured by following the time course of differential 14 CO 2 and 12 CO 2 uptake. At 8 mg O 2 L −1 (equal to oxygen saturation at 20 °C), the rate was 0.4 μg C (mg organic dry weight) −1 h −1 , which was about 10% of net photosynthesis under the experimental conditions. Increasing the oxygen concentration to 30 mg O 2 L −1 , enhanced photorespiration to 30% of net photosynthesis. It was shown that the concentration of oxygen affected net photosynthesis, CO 2 evolution into CO 2 -free water in the light, the post-illumination CO 2 burst, and the CO 2 compensation point.The effect of the internal gas space on recycling of CO 2 was investigated by comparing gas-exchange by intact and sectioned leaves. About 30% of the CO 2 of photorespiratory origin was recycled internally within the lacunal system. The gas-exchange characteristics of Scirpus were similar to those observed in terrestrial C 3 species although of a minor magnitude and a different time course. The ecological implications of these finds are discussed.