Oxygen and radiation effects on C02 exchange in fight and in darkness of decaploid and hexaploid tall fescue (Festuca arundinacea Schreb.)

Abstract

Rates of apparent photosynthesis (APS). photorespiration (PR), CO<sub>2</sub> compensation (I) and dark respiration (DR) were determined on attached shoots of decaploid (70 chromosomes) and a hexaploid (42 chromosomes) genotype of tall fescue (Festuca arundinacea Schreb.) using an infra red CO<sub>2</sub> analyzer arranged in a closed circuit system. Plants were grown at a photon flux density 500 µmol m<sup>-2</sup>s<sup>-1</sup> (400-700 nm) and at 25°C. Measurements were made at 25°C in O<sub>2</sub> concentrations of l, 21 and 100% and at irradiance of 500 or 1800 µmol m<sup>-2</sup>s<sup>-1</sup>. The decaploid exhibited rates of APS that was from 26 to 46% higher in 1 and 21% O<sub>2</sub> but not in 100% O<sub>2</sub>, than those of hexaploid. Rates of PR were positively related to rates of APS. Values of r were very similar for both genotypes, they were little affected by irradiance, and were a linear function of O<sub>2</sub> Concentration. The percentages of PR in true photosynthesis (TPS = APS+ PR) were also similar for the two genotypes, and were a linear function of O<sub>2</sub> concentration. Alternatively, rates of DR were by 16-26% higher in the hexaploid than decaploid genotype, and were little affected by O<sub>2</sub> concentration or by previous rates of APS.