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), CO₂ 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 CO₂ analyzer arranged in a closed circuit system. Plants were grown at a photon flux density 500 µmol m^-2s^-1 (400-700 nm) and at 25°C. Measurements were made at 25°C in O₂ concentrations of l, 21 and 100% and at irradiance of 500 or 1800 µmol m^-2s^-1. The decaploid exhibited rates of APS that was from 26 to 46% higher in 1 and 21% O₂ but not in 100% O₂, 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 O₂ Concentration. The percentages of PR in true photosynthesis (TPS = APS+ PR) were also similar for the two genotypes, and were a linear function of O₂ concentration. Alternatively, rates of DR were by 16-26% higher in the hexaploid than decaploid genotype, and were little affected by O₂ concentration or by previous rates of APS.