pH values and redox potentials in microsites of the rhizosphere

Redox potentials (Eh) and pH values in the rhizosphere 0–2 mm from growing roots of field beans ( Vicia faba L.) indicated reducing conditions near the root tip and along the zone of elongation which were probably caused by root exudates. For roots of other plant species (e.g. maize), a drop of Eh in the rhizosphere does not necessarily reflect reduction processes, but may be due to pH changes, according to the Nernst equation. Eh values near dying roots decreased due to the O 2 consumption by microorganisms, this effect being detectable at a distance greater than 3 mm from the root surface.