Symbiosis of Leguminous Plants and Nodule Bacteria: V. The Growth of Red Clover at Different Oxygen Tensions

A comparison has been made of the effect of oxygen concentrationon the growth of nodulated red clover plants dependent on nodule-nitrogenand of non-nodulated plants provided with ammonium-nitrogen.Two techniques have been used, the first providing for the exposureof the root system only to adjusted oxygen supply, while inthe second the whole plant was so exposed. Four levels of oxygenwere employed, namely, 21, 12, 5, and 1 per cent. With the first method each step in the reduction of oxygen supplywas attended by a significant curtailment of growth in nodulatedplants. The responses of the ammonium plants were less marked.It is concluded that clover nodules function best when wellsupplied with oxygen. No clear effects of oxygen supply were obtained by the secondmethod, this being due, it is considered, to the severe limitationimposed by the necessary experimental arrangement on the growthof the plants.