GROWTH AND NUTRIENT ACCUMULATION AS CONTROLLED BY OXYGEN SUPPLY TO PLANT ROOTS

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Abstract
Attention was focused on the response of several plants to low oxygen partial pressures in the root zone. Gaseous nitrogen-air mixtures from 0.5 to 6.4% were obtained with a special apparatus for maintaining constant gas composition. Changes in leaf elongation, green wt., and ion accumulation, and shifts in the internal nutritional status of the shoot, were observed over a 2-week period. Transport of P32 and K42 isotopes was studied over 2- to 3-day periods. Root growth of all plants was stopped at an oxygen content of 0.5% in the gas ambient to the roots. Top growth and ion accumulation continued at this level. Rate of transfer of P32 from the root to the shoot of tobacco was independent of aerobic mechanisms in the root. Transfer of the trace elements B, Cu, Al, and Na from the low concn. of the medium to higher values in the shoot appeared not to depend upon an aerobic mechanism. The increase in Na concn. at low oxygen partial pressures was striking in all plants. Accumulation of major nutrients, with the exception of Mg for tomato, paralleled top growth in dependence upon oxygen supply to roots.