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Determination of Root Exudates in a Steril Continuous Flow Culture. II. Short-Term and Long-Term Variations of Exudation Intensity ¹

Institut fuer Bodenkunde der Georg August Universitaet, Goettingen, Germany

The exudate production of alfalfa under the conditions of the sterile flow culture was quantitatively measured. In the first 40 days 3.10^–3 µmoles amino-N, 2.5 µequivalents of organic acids and approximately 10^–4 µmoles of reducing sugars were liberated per plant and per day into the percolating nutrient solution. The amino acid concentration in the outflow varies according to a daily periodicity. The exudation of a colored substance also shows daily periodical variations. This pattern is different from the pattern of the amino acid exudation, however, and directly coupled to shoot illumination. Short-term 2,4-dinitrophenol additions to the nutrient lower the liberation of amino acids into the percolating solution.