Fig. 2 (a) Orthophosphate concentration (Cp) and (b) pH in solution of rock phosphate (no-clay) suspensions as a function of equilibration time. Inoculation took place at t = 24 h. An asterisk (*) represents a significant difference (t test comparison, P < 0.05) between biotic (E37) and abiotic (no E37) treatments at given time and initial pH treatment