ROOT GROWTH AND DARK FIXATION OF CARBON DIOXIDE IN CALCICOLES AND CALCIFUGES

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Abstract
Summary: The inhibition of root growth by bicarbonate ions has been further investigated by an examination of the process of dark fixation of carbon dioxide by Arrhenatherum elatius and Deschampsia flexuosa. Excised roots incorporated [14C]bicarbonate mostly into malate in 4 hours. Intact plants grown on solutions containing 10 m‐equiv./1 bicarbonate for 24 hours showed large increases in the total acid content of the roots. Malate was increased in both species and citrate also in Arrhenatherum elatius. The increases in total acidity were similar and could be explained solely by the dark fixation of bicarbonate. Seedlings grown on solutions of sodium hydrogen malate showed similar inhibitions to those observed on sodium bicarbonate solutions. Root growth of Deschampsia flexuosa was inhibited throughout a range of malate concentrations (1–20 m‐equiv./l) whereas Arrhenatherum elatius was stimulated at low malate concentrations and only slightly inhibited at 20 m‐equiv/1. The inhibiting action of bicarbonate on the root growth of Deschampsia flexuosa is associated with the increase in malate in the roots by dark fixation. The results are discussed in terms of the organic acid content and metabolism of calcicole and calcifuge species.