Fig. 2.
Effects of carboxylates (and other exudates) on inorganic phosphorus (Pi) and organic P (Po) mobilization in soil. Carboxylates are released via an anion channel. The exact way in which phosphatases are released is not known. Carboxylates mobilize both inorganic and organic phosphorus. Phosphatases hydrolyse organic phosphorus compounds, once these have been mobilized by carboxylates. Carboxylates will also mobilize some of the cations that bind P. Some of these cations (especially Fe) move to the root surface for uptake by the roots. Others move down the soil profile, where they are thought to give rise to the formation of laterite (in the case of Fe) (Pate et al., 2001; Verboom and Pate, 2003) or other precipitates (in the case of Al or Ca) (Verboom and Pate, 2006).