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Oxygen Diffusion in the Soil-Plant System II. Respiration Rate, Permeability, and Porosity of Consecutive Excised Segments of Maize and Rice Roots¹

Respiration rates were determined at 4.4, 20.8 and 30% oxygen concentration for consecutive excised segments of maize (Zea mays L.) and rice (Oriza sativa L.) roots. From these data, the maximum respiration rate, the oxygen concentration at which respiration was half of the maximum rate, and the root permeability to oxygen were derived for each position along the root, up to 10 cm from the root tip for maize and 6 cm for rice. The gas-filled porosity of these segments was measured by the pycnometer method.

The root tip segment is characterized by the highest maximum respiration rate, highest permeability, and lowest porosity. Both respiration rate and permeability decrease with distance from the root tip, whereas porosity increases to a maximum of 10% for maize and 33% for rice. The oxygen concentration at which respiration is half of the maximum rate is about 8% for maize and about 16% for rice at each position along the root.

Key Words: Root respiration • Root permeability • Root porosity • Excised root segments

² Research Assistant and Professors of Soil Physics, respectively.

Received for publication June 27, 1969.

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