Photosynthesis and chlorophyll fluorescence in tall fescue

Measuring the photosynthetic rate of tall fescue (Festuca arundinacea) at low temperatures is difficult because dew or frost on the leaves often prevents the use of a CO2 analyzer. Chlorophyll fluorescence measurements may make it possible to estimate photosynthetic potential when it is impossible to make photosynthetic measurements. Chlorophyll fluorescence parameters used were Fo, minimum fluorescence yield, and Fm, the maximum fluorescence yield. Fv, the variable fluorescence, is the difference between Fm and Fo. The efficiency of energy conversion in photosystem II is estimated from the ratio Fv/Fm. Poskuta and Waclawzyk (1995) found that the toxic effect of lead in tall fescue leaves occurred much sooner on apparent photosynthesis and photorespiration than on photosystem II activity as measured by the Fv/Fm ratio. Okawara and Kaneko (1995) reported that Fv/Fm values were relatively constant from early September to late November. The objectives of this experiment were first, to compare the chlorophyll fluorescence ratio Fv/Fm, photosynthetic rate, and stomatal conductance among three tall fescue cultivars free of the endophyte (Acremonium coenophialum) and endophyte-infested Kentucky 31 in spring and fall. The second objective was to relate the chlorophyll fluorescence ratio Fv/Fm with photosynthetic rate and stomatal conductance in the spring and fall.