14c-Labelled material leached from the rhizosphere of plants supplied with 14CO2

Abstract

14C, supplied to plant tops as 14CO2, was recovered in water-soluble organic material when pots with wheat, clover, or ryegrass growing in a podzolic sand were leached with distilled water at weekly intervals following exposure to 14CO2. Similar material was recovered from unplanted controls. Percentage recoveries of total 14C supplied were ryegrass 0-41, clover 0,30, wheat 0,19, control 0-14. 14C was leached from all pots at a steady rate up to 10 weeks following cessation of exposure to 14CO2. 14C was not detected in such compounds as sugars or amino acids and fractionation with Sephadex gels and ultrafiltration indicated a molecular weight distribution of not less than 700 to more than 10,000. 14C was strongly retained by anion-exchange resin and was probably associated with components ofthe fulvic acidhumic acid complex. The evidence did not favour 14C in leachates arising directly from the metabolism or decomposition of roots. It is proposed that 14C was incorporated into soil microflora by assimilation of organic compounds released from roots or by heterotrophic fixation of CO2, with subsequent release following metabolism or death or both of individual cells. Defoliation of ryegrass previously exposed to 14CO2 increased the amount of 14C in leachates, with more than 20% apparently contained in polysaccharides. © 1971 CSIRO.