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

Abstract

From the viewpoint of the efficient use of light in photosynthesis, algae possess the advantage (over higher plants) that the medium in which they grow can be readily enriched with bicarbonate, and growth correspondingly increased. For higher plants, un-fortunately, it would hardly be possible to enrich the atmosphere appreciably with CO2. However, it oc-curred to one of us that it might be practical to en-rich the soil or the nutrient solution (17). One or two unsuccesful attempts at this have been made in the past, but without any-systematic study of the factors involved.4 Recent claims of increased yields following carbonate fertilization, by Kursanov and co-workers in Russia (see below) make a study of this problem more urgent. Such a practice would depend critically on whether roots can absorb CO2 or bi-carbonate to an appreciable extent. The present work was therefore undertaken to determine the amount of CO or bicarbonate which could be absorbed by the roots of intact plants, and to study the effect of CO2, applied in the root medium, on the growth of the root system and of the whole plant. Both monoco-tyledons and dictyledons have been included in the experiments. It is known, of course, that roots, like other non-green tissues, are capable of fixing CO2. Ruben and Kamen (14) demonstrated uptake of C1102 by a preparation of ground barley roots as long ago as 1940, but the short half-life of the isotope used pre-vented identification of the compounds into which the CO2 was incorporated. Overstreet, Ruben and Broyer studied the uptake of bicarbonate ions by ex-cised barley roots over a short period (11). Their data allow an approximate comparison of the amounts taken up with the amount produced by respiration; with their "low-salt" plants, using KHC1303 as bi-carbonate source, it develops that the uptake repre-sented abouit 10 % of respiration. However, the amount of K+ taken up was three to six times as large as the amount of HCO3-taken up in the same length of time. MIore recently, Poel (12) has repeated and extended these experiments, using C14 and radio-chromatographic techniques, and has identified the products of fixation as malic, citric, aspartic and glutamic acids, serine, asparagine, glutamine and tyrosine, with a very little a-keto-glutaric acid. 1 Received February 12, 1957. 2 Maria Moors Cabot Research Fellow, on leave of