THE IMPORTANCE OF OXYGEN IN THE NUTRIENT SUBSTRATE

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Abstract
The rate of respiratory C02 produced by soybean, oat, and tomato roots grown in a basal nutrient soln. adequately supplied with nitrate N (plus-N cultures) was always higher than that of the roots of corresponding cultures grown without N (minus-N cultures). The substitution of ammonium N for nitrate N in the nutrient substrate also produced lower yields of respiratory CO2 than did corresponding cultures supplied with nitrate N, the values approaching those obtained with minus-N cultures. The difference between the respiratory CO2 produced by the plus-N roots and the minus-N roots (extra CO2) is greatest at lowest oxygen levels and follows very closely the curves of nitrate-ion absorption and nitrate reduction as influenced by a wide range of oxygen levels in the nutrient substrate. The production of the extra CO2 appears to be directly associated with the evolution of oxygen in nitrate reduction and its utilization in the respiratory processes.