Microbial Inorganic Polyphosphates: Factors Influencing Their Accumulation in Soil

Infrared spectra of microbially synthesized, acid labile, inorganic P compounds extracted from soils provided additional evidence that they are inorganic polyphosphates (poly P). Incubation studies with glucose amended soils demonstrated the transient nature of naturally occurring poly P. Experiments are reported on the conditions which optimize poly P synthesis in soil. A 2‐week incubation period (preincubation) with a source of carbon (2% glucose or 4% straw) and a further 2‐day incubation period (postincubation) after adding a source of ortho P resulted in the maximum accumulation of poly P. The quantity of poly P also increased with increasing rates of orthophosphate from none to 1,000 µg soil/g. Longer periods of postincubation reduced poly P accumulation. Poly P synthesis was greater when relatively insoluble sources of P were added to soils and accumulation followed the order; FePO 4 · 2H 2 O > rock phosphate > Ca(H 2 PO 4 ) 2 · H 2 O > KH 2 PO 4 . These results suggest that poly P synthesis may accompany P solubilization in soils and be an integral part of the soil P cycle.