THE INFLUENCE OF PLANT ROOTS ON AUTOTROPHIC NITRIFYING BACTERIA

An investigation of the effects of corn and alfalfa roots on Nitrosomonas and Nitrobacter showed a stimulation of these organisms in the rhizosphere at 15 days but not at 46 days. A rapid method of estimating Nitrosomonas populations in soils was developed which depends on the color change in brom-thymol blue with the fall in pH associated with nitrite production.In liquid media alfalfa root exudate inhibited Nitrosomonas at high concentrations but had no effect on the growth of Nitrobacter. Corn root exudate also inhibited Nitrosomonas but its effect on Nitrobacter was to reduce the duration of the lag phase without changing the generation time.