Diurnal Variation in Nitrogenous Constituents of Alfalfa (Medicago sativa L.)1
- H. W. Youngberg,
- D. A. Holt and
- V. L. Lechtenberg2
Alfalfa (Medicago sativa L.) was sampled eight times daily for 3 days during a third growth period in order to detect diurnal changes in concentrations of various classes of nitrogenous constituents. The implications of these changes with regard to N metabolism were considered.
Total N was determined by predigesting forage samples with salicylic-sulfuric acid and assaying with the Nessler reagent. Total water-soluble N was determined by performing the same procedure on aqueous extracts of the tissue. Nitrate N was assayed by the phenol-disulfonic acid procedure. Ninhydrin was used to determine amino N. Potassium concentration in an acid digest of tissue was measured spectrophotometrically. Analyses were performed on leaflets and on stems and petioles.
The percentages of total N, water-soluble N, amino N, and K in alfalfa leaves and stems were highest between 3 and 6 AM and declined through the light period during 3 days of frequent sampling in the field. Nitrate N in alfalfa stems followed a similar trend, but there was no diurnal change in nitrate concentration in leaves.
Nitrogen compounds are diluted during each light period by the considerable amount of nonstructural carbohydrate synthesized. This probably accounts for the observed decline in percentage of nitrogenous constituents.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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