Influence of soil acidity on the occurrence of Athiorhodaceae

Enrichment cultures from strongly acid Sphagnum bog peats and moderately acid to circumneutral fen peats revealed Athiorhodaceae to be present in almost all suitably wet samples above pH 5.3 and absent from almost all samples below pH 4.7. These bacteria were recorded in only one of the fifty cultures from acid humus layers in a jack pine forest, and in none of thirty cultures from moderately acid humus layers in a mixed woodland. They were also absent from old-field surface soils, which often contained considerable amounts of organic litter.