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.

Keywords

• Festuca arundinacea Schreb.
• photosynthesis
• photorespiration
• dark respiration
• CO2 compensation point