Irradiance Response of Tall Fescue Genotypes with Contrasting Levels of Photosynthesis and Yield¹

Abstract

The purpose of this study was to determine if genotype by irradiance interactions or genetic variation in diurnal trends of CO2 exchange rate (CER) influenced the CER‐yield relationship in tall rescue (Festuca arundinacea Schreb.). Genotypes were selected in the field for high CER‐high yield, high CER‐lowyield, low CER‐high yield, and low CER‐Iow yield. Responses of CER to photosynthetic photon flux density (PPFD) of these genotypes were determined using both growth chamber‐ and field‐grown material. The shapes of the PPFD response curves were similar for all genotypes, and saturation occurred at approximately 1,200 μE m‐2 sec‐1 (400 to 700 nm) under both growth conditions. In a growth chamber at 25/20 C (light/dark), all genotypes achieved near maximal CER and photorespiration within 1 hour of the beginning of the photoperiod and maintained these rates throughout the rest of the photoperiod, with high CER genotypes exhibiting about 30% higher rates than low CER genotypes. Photorespiration rates were significantly correlated (r = 0.80) with CER. Leaf diffusive resistance were similar for all genotypes throughout the photoperiod.Genotypic differences did not occur in PPFD‐response curves or diurnal patterns of CER. This suggests that differences in these two factors among genotypes are not the underlying cause of the poor relationship reported between short term measurements of leaf photosynthesis on recently collared leaves and forage yield. Other factors must be limiting genetic expression for CER in terms of yield.

Leaf Growth, Leaf Aging, and Photosynthetic Rate of Tall Fescue Genotypes1

“…In the growth chamber, leaf growth rates of high-yielding genotypes were 54y0 greater than low-yielding genotypes. T h e highest yielding genotype in these studies, L-H, (Wilhelm and Nelson, 1978) was consistently high in leaf growth rate, which supports the conclusion of Horst (1973) that leaf growth rate was closely associated with forage yield.…”

“…They suggested that factors such as genotypic variation in leaf aging and canopy architecture may have a dominant influence on dry matter production of each genotype, regardless of CER. Wilhelm and Nelson (1978) selected genotypes of tall fescue with combina- 'Contribution from the Missouri Agric. Exp.…”

“…Four genotypes of tall fescue were selected (Wilhelm and Nelson, 1978) to represent four CER-yield categories: high CER-high yield (H-H), high CER-low yield (H-L), low CERhigh yield (L-H), and low CER-low yield (L-L). For two separate experiments, three vegetative tillers of each genotype were planted in 10-cm diam by 15-cm deep plastic pots filled with Mexico silt loam top soil.…”

“…Plots had been established on a Mexico silt loam (Udollic Ochraqualfs; fine, montmorillonitic, mesic) and originally consisted of 33 sprigs of each genotype in three rows 25 cm apart, with plants 15 cm apart in the rows (Wilhelm and Nelson, 1978). Plots were arranged in a randomized, complete block design with four replications and had developed a sward condition.…”

Growth Analysis of Tall Fescue Genotypes Differing in Yield and Leaf Photosynthesis1

“…Genotypes used in this study were originally selected for early flowering. Yield and CER of these genotypes were originally determined in field studies during 1972 and 1973 and are described by Wilhelm and Nelson (1978a). In general, the high category genotypes had about 30% greater CER and 32y0 greater yield than did the low category genotypes.…”