PHOTOSYNTHESIS, RESPIRATION, AND ORGANIC-CARBON RELEASE IN ELODEA-CANADENSIS MICHX

Photosynthesis, respiration, and release of organic carbon were examined using 14C in the freshwater angiosperm Elodea canadensis Michx. to investigate ecophysiological implications of recent biochemical evidence for significant levels of C4 photosynthesis in this plant, a pathway normally associated with low photorespiration and high photosynthetic efficiency. Photosynthetic light saturation level was somewhat high, but not in the normal C4 range. In morning and afternoon in situ experiments with oxygen manipulations, the plant exhibited an afternoon depression of net photosynthesis suggestive of C3 performance. Organic carbon release was significant and may have included glycolate, but photorespiration as oxygen-sensitive loss of carbon dioxide in the light was not demonstrable, and the carbon dioxide compensation point was very low and oxygen-insensitive, consistent with C4 efficiency. Thus the plant, while not a C4 species, appeared to have some responses consistent with partial operation of the C4 pathway, which may contribute to the frequent competitive superiority of the plant. © 1979.