Diurnal Variation in Nonstructural Carbohydrates of Festuca arundinacea (Schreb.) With and Without N Fertilizer1
- V. L. Lechtenburg,
- D. A. Holt and
- H. W. Youngberg2
The purpose of this research was to (i) define in detail, under field conditions, the normal diurnal accumulation and depletion pattern of the various nonstructural carbohydrates in tall fescue (Festuca arundinacea Schreb.) herbage and (ii) investigate the influence of N fertility on diurnal variation in these carbohydrates. The implications of these daily trends with regard to forage management and quality and to carbohydrate metabolism in this species were considered.
Tall fescue herbage was sampled several tunes daily during first and second growth periods. Reducing sugars and sucrose were extracted from freeze-dried, ground herbage with alcohol. Next, fructosan was removed by water extraction, and the residue from these extractions was treated with 0.2 N sulfuric acid to hydrolyze other nonstructural polysaccharides. Ferricyanide, resorcinol, and phenol-sulfuric acid procedures were used to quantitatively assay sugars in the extracts. The daily trends in various carbohydrates were analyzed statistically using orthogonal regression techniques.
During the first growth period the average sugar percentage of leaves and stems increased from 8.2% at 6 AM to 10.3% at 6 PM. Sucrose accounted for most of the increase with some diurnal variation in percent glucose. Percent fructose did not vary significantly. In the second growth forage only sucrose varied significantly, increasing from 2.7% at 6 AM to 5.1% at 6 PM. Thirty-seven percent of the daily increase in sucrose was respired or translocated between 6 PM and 12 M, while 63% was utilized after midnight. Fructosan concentration did not vary diurnally during either growth period.
Nitrogen fertilization reduced the average fructosan concentration from 7.3 to 0.4% of the dry weight in the first growth and from 1.6 to 0.5% of the dry weight'in the second growth forage. Fructosan accumulated in the unfertilized forage as the first growth period progressed. Nitrogen fertilization did not influence the average amount of reducing sugars present during either growth period. Sucrose content was reduced by N during the first but not the second growth period. Diurnal trends were not affected by N fertilization.
Acid (0.2 N H2SO4)-soluble carbohydrate percentage, which consisted primarily of pentosan, varied diurnally during the first growth period. Nitrogen fertilization reluced this fraction from 12.6 to 7.3% during the first growth period and from 10.3 to 6.5% during the second growth period.
To the extent that carbohydrates contribute to the acceptability of a forage or that a forage is lacking in energy, N fertilization may decrease forage quality. Yield and other quality factors enhanced by N fertilization may compensate for carbohydrate losses.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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