The Absorption of Ions by Excised Root Systems

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Abstract
An apparatus is described by means of which the absorption of ions from a complete nutrient solution of constant composition by excised root systems of plants, grown under known nutrient deficiencies, may be measured in standard conditions of aeration and temperature. Results of some prelimi nary experiments are described. It was found that the roots readily absorbed the element in which they were deficient, but tended to lose those elements which were already present in normal amounts. There was almost invariably a loss in fresh weight of the roots after the absorption period and also a loss in dry weight. This loss appears to be complex and is partly attributable to loss of respiratory material. The addition of 2 per cent. sucrose to the solution from which the root systems of phosphorus-deficient barley plants were absorbing increased the nitrogen and phosphorus contents of the roots and maintained the potassium content, while in absence of sucrose only the phosphorus content increased, but this increase was significantly less than in the presence of sucrose. It was shown that roots excised from plants growing in soil were capable of absorbing phosphorus or nitrogen—elements in which they were apparently deficient. The interpretation of data obtained from excised roots is discussed, and it is concluded that excised roots from plants grown in complete nutrient are not likely to behave in the same way, as regards absorption, as corresponding roots of intact plants, but that roots grown under conditions of deficiency will behave rather similarly whether excised or intact. This fact provides a potential method for diagnosing and evaluating nutrient deficiencies. The low-salt condition of roots postulated by Hoagland and Broyer is not necessarily the primary requisite for rapid absorption of a particular ion. It is rather that the roots should be deficient in that ion. The roots could be high in other salts.

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