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Agronomy Journal Abstract -

Growth and Photosynthate Partitioning in Alfalfa Under Eight Temperature-Photosynthetic Period Combinations1


This article in AJ

  1. Vol. 73 No. 3, p. 392-394
    Received: Mar 11, 1980

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  1. N. J. Chatterton and
  2. G. E. Carlson2



A characterization of the growth responses of high and low yielding alfalfa (Medicago sativa L.) plants to environmental parameters will provide important information on their yield potential. This experiment was conducted to determine if growth temperature and length of the photosynthetic period mediate the differential herbage yielding abilities of alfalfa genotypes previously selected under field conditions for high and low herbage yield. Twelve genotypes were grown at 20/15, 23/18, 26/21, and 29/24 C day/night temperatures in 10-hour and 14-hour photosynthetic periods in controlled environments. Dry weights and total nonstructural carbohydrate percentages were obtained on herbage and root tissues. Carbon dioxide exchange rates were measured using infrared gas analysis on attached leaves and expressed on a per unit leaf area and a per unit leaf dry weight basis. Relatively large herbage yield differences previously observed among the various clones under field conditions were minimized in all treatments when plants were grown in controlled environments where moisture and nutrient stresses were assumed to be minimal. The apparent diurnal accumulation rate of total nonstructural carbohydrates was faster in the herbage of plants grown in short photosynthetic period conditions than in those grown in long ones. Such a relationship suggests an influence on photosynthate partitioning by length of the daily photosynthetic period. We conclude that yield differences observed under field conditions were not necessarily related to differential responses to either temperature or length of the daily photosynthetic period. Furthermore, photosynthesis, as measured by single leaf CO2 exchange rate, was not positively correlated with herbage yield under the various controlled environmental conditions used in this experiment.

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