On the Uptake of Carbon Dioxide and Bicarbonate by Roots, and Its Influence on Growth.

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Abstract
Growth of roots of Pisum sativum, Vicia Faba, Phaseolus vul-garis and Helianthus annuus is completely inhibited if the root medium is aerated with 6.5% CO2 in air. Avena sativa and Hordeum vulgare are almost unaffected by such a treatment. Peas show a small but consistent stimulation of root growth when the root atmosphere contains 0.5% CO2, but are clearly inhibited at levels as low as 1.5%. Some possible explanations of the difference in sensitivity to CO2 of peas and barley have been ruled out, and a specific toxic effect seems indicated. The effect is apparently exerted by CO2 itself, rather than by bicarbonate ions. The uptake of CO2 by the roots of both peas and barley is of the order of only a few percent of the amount produced by respiration in short term experiments, and it virtually ceases after about 8 hours. The bulk of COo fixed was converted to malic and citric acids and sugars; after 24 hours only about 10% had entered the alcohol-insoluble fraction. Translocation of the products into the shoots of the intact plant was about 3 times as great in the light as in the dark. However, it seldom reached as high as the amount in roots. It is concluded that carbonate fertilization of crops is unlikely to be beneficial, and that the CO2 content of some soils may, indeed, already be supra-optimal. Recent Russian claims for increased yields following carbonate fertilization are discussed in the light of the present work.