Studies of Rhizosphere Activity by the Use of Isotopically Labelled Carbon

Abstract

In an attempt to assess the microbiological activity characterizing the microflora associated with the roots of tomato plants, experiments were performed in which C1402 was supplied to their leaves and subsequently the soil was sa~npled for radioactivity. Several varieties of tomato were tested, some of which were resistant and some susceptible to Verlicillium albo-alrzrm. 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 HC1 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 Verlicillizrm-resistant and -susceptible plants, although individual varieties seemed t o be characterized by fairly definite patterns of radioactivity.In spite of its limitations, the technique of plating serial dilutions of soil extracts has added exteilsivelv to our knowled~e of the rhizos~here and its -effect on crop plants. I t has been used also in assessing the relative status of rhizosphere microfloras in different cultivars of several crop plants with dif-

14c-Labelled Material Leached From the Rhizosphere of Plants Supplied with 14co2

“…The release of 140-labelled molecules from plant roots following exposure of the tops to 14 002 has been reported for plants grown in sterile solution culture (McDougall and Rovira 1965;Slankis, Runeckles, and Krotkov 1964) and in untreated soil (Subba-Rao, Bidwell, and Bailey 1962). The latter studies showed that appreciable amounts of radioactivity could be leached from funnels containing young tomato plants growing in a garden soil within 12 hr of exposing the plants to 14 002.…”