Photosynthesis, Photorespiration and Respiration of Detached Spruce Twigs as Influenced by Oxygen Concentration and Light Intensity

Abstract

AbstractThe effects of oxygen concentration and light intensity on the rates of apparent photosynthesis, true photosynthesis, photorespiration and dark respiration of detached spruce twigs were determined by means of an infra‐red carbon dioxide analyzer (IRCA). A closed circuit system IRCA was filled with either 1 per cent of oxygen in nitrogen, air (21 % O2) or pure oxygen (100 % O2). Two light intensities 30 × 103 erg · cm −2· s−1 and 120 × 103 erg · cm−2· s−1 were applied.It has been found that the inhibitory effect of high concentration of oxygen on the apparent photosynthesis was mainly a result of a stimulation of the rate of CO2 production in light (photorespiration). In the atmosphere of 100 % O2, photorespiration accounts for 66–80 per cent of total CO2 uptake (true photosynthesis). Owing to a strong acceleration of photorespiration by high oxygen concentrations, the rate of true photosynthesis calculated as the sum of apparent photosynthesis and photorespiration was by several times less inhibited by oxygen than the rate of apparent photosynthesis. The rates of dark respiration were essentially unaffected by the oxygen concentrations used in the experiments. An increase in the intensity of light from 30 × 103 erg · cm−3· s−1 to 120 · 103 erg · cm−2· s−1 enhanced the rate of photorespiration in the atmospheres of 21 and 100 % oxygen but not in 1 % O2. The rate of apparent photosynthesis, however, was little affected by light intensity in an atmosphere of 1 % oxygen.