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Shade Effects on Growth of Tall Fescue: II. Leaf Gas Exchange Characteristics

Dep. of Agronomy

S. G. Pallardy

School of Natural Resources, Univ. of Missouri, Columbia, MO 65211

*Corresponding author.

The irradiance environment during development affects the elongation rate and photosynthetic capacity of leaves. Our objective was to determine the effect of shade during development on stomatal and nonstomatal factors affecting photosynthesis. Vegetative plants of tall fescue (Festuca arundinacea Schreb.) were grown outdoors in pots during summer of 1986 and autumn of 1987. Irradiance treatments were provided by shading the plants with neutral-density screencloth during a 10-wk growth period. Gas exchange characteristics of the youngest fully expanded leaf blades were measured. Irradiance required for saturation of CO₂ exchange rate (CER) at 340 µL L^-1 ambient CO₂ was 1000 to 1200 µmol m² s^–1 of photosynthetic photon flux density when plants were grown at low irradiance (30% full sun) compared with 1500 µmol m^–2 s^–1 when grown at high irradiance (full sun). The CER per unit leaf area, measured at irradiance saturation, was 25% lower in 1986 and 14% lower in 1987 for leaves grown in low irradiance compared with leaves grown in high irradiance. Stomatal conductance to CO₂ decreased similarly, causing internal CO₂ concentration at irradiance saturation to be similar among treatments. When CER was expressed per unit dry weight or per mesophyll cell volume, no difference was observed between treatments. The adaptation to low irradiance of both leaf anatomical and physiological processes affecting photosynthesis was well coordinated; net CO₂ uptake was decreased, but relative stomatal and nonstomatal limitations were not altered.

Received for publication January 8, 1990.

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