Photosynthesis and Degree of Polymerization of Fructan during Reproductive Growth of Meadow Fescue at two Temperatures and two Photon Flux Densities

Abstract

Accumulation of dry weight was measured in plant parts of meadow fescue (Festuca pratensis Huds.) that was grown at 16/11 °C or 26/21 °C and with 20 or 60 nE cm⁻² s⁻¹ photosynthetically active radiation. Plants reached anthesis about 3 weeks later at 16/11 °C than at 26/21 °C and had then a higher proportion of dry weight in inflorescences and less in leaf blades. Growth temperature had little effect on CO₂ exchange rate (CER) but plants grown at 60 nE cm⁻² s⁻¹ had higher CER than those grown at 20 nE cm⁻² s⁻¹. The concentration of water-soluble carbohydrates (WSC) at similar growth stages was usually higher at 16/11°C than at 26/21°C. High radiation also led to higher WSC in stem and leaf tissue. Root tissue changed least and WSC did not exceed 10% of dry weight during the experiment. In all tissues, when WSC was high, the fructans were distributed into a group with a high degree of polymerization (DP) and another with a low DP. The low DP group included sucrose, reducing sugars and fructans up to about 20 units long. An apparent threshold concentration of WSC was necessary for synthesis of the high DP fructans. This concentration was near 12% for leaf tissue, about 6% for stem base tissue, and 2.5% for root tissue. The average apparent DP of the high DP fructan group was 43 to 50 for leaf tissue, 31 to 93 for stem base tissue, and 27 to 31 for roots. These characteristics appeared to be mostly tissue dependent with less effect from temperature and radiation.