Photorespiration and productivity in submersed aquatic vascular plants1

Abstract

A 14 C assay for photorespiration (the light‐induced uptake of oxygen and release of carbon dioxide resulting from glycolate metabolism) was developed for use with submersed aquatic plants. Laboratory studies with axenic cultures of Najas flexilis (Willd.) Rostk. and Schmidt indicated that respired carbon dioxide is refixed extensively in the light and that the 14 C assay is a measure of net, rather than gross, photorespiration. Analyses of leaf anatomy and early 14 C fixation products of photosynthesis indicated that N. flexilis is a C 3 plant with Calvin‐Benson cycle photosynthesis and glycolate metabolism. Respiration in the light in axenic N. flexilis increased with increasing dissolved oxygen concentration, which indcated the presence and enhancement of photorespiration and that net photosynthesis would decrease with increasing oxygen concentration. In situ experiments with N. flexilis and Scirpus subterminalis demonstrated variations in photorespiration and dark respiration within a 1‐day photosynthetic period and seasonally.