STUDIES OF RHIZOSPHERE ACTIVITY BY THE USE OF ISOTOPICALLY LABELLED CARBON

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Abstract
In an attempt to assess the microbiological activity characterizing the microflora associated with the roots of tomato plants, experiments were performed in which C14O2 was supplied to their leaves and subsequently the soil was sampled for radioactivity. Several varieties of tomato were tested, some of which were resistant and some susceptible to Verticillium albo-atrum. Radioactivity in varying amounts was found in soil eluates, so that carbon fixed in photosynthesis must have passed out of the roots into the soil. Some of the radioactivity was released from the soil only by alcohol extraction and HCl hydrolysis and this fraction is considered to have been fixed in soil microorganisms as a result of their metabolic activity. The techniques used did not differentiate between the microbiological activities associated with Verticillium-resistant and -susceptible plants, although individual varieties seemed to be characterized by fairly definite patterns of radioactivity.