Inhibition of Nitrite-Oxidizers by Roots of Grass

Abstract

A heat-labile substance in the roots of Hyparrhenia filipendula is toxic to nitrite-oxidizers. The inhibitor seems to be present in the outer tissues of the roots thoughout the year, and in the summer (Nov.-Feb.) it is found in the stele as well. (Jan. and Feb. are usually the wettest months of the year and at this time the grass is growing vegetatively and flowering.). Viable cell counts shows that the inhibitor is bactericidal, not merely bacterio-static. As the inhibitor is soluble in the culture medium it is probably water-soluble. This inhibitor may account for the small number of ammonia- and nitrite-oxidizers in African grassland soils.