Substrate Flow and Utilization in the Rhizosphere of Cereals

SUMMARY Wheat and barley plants were grown for 3 weeks with their roots in sterile or non‐sterile sand or irrandiated or non‐irradiated soil and with their shoots in an atmosphere containing 14CO2 at constant specific activity and at approximately atmospheric concentration. The sealed pots were regularly flushed with air and the total quantity of radioactivity lost from the pots as respiratory 14CO2 and the amounts present in the plant rhizoplane, rhizosphere and bulk soil were analysed. Measurements of bacterial numbers allowed calculations of the utilization of the carbon released from the roots of the sand‐grown plants. The relevance of the techniques used and the implications of carbon loss for the plant and associated microorganisms are discussed.