THE ROLE OF CALCIUM OXALATE IN THE AVAILABILITY OF PHOSPHORUS IN SOILS OF SEMIARID REGIONS

Abstract

Evidence is presented for the presence of Ca-oxalate crystals at the soil-hyphae interface of mycorrhizal Pascopyrum smithii. This prompted the development of a thermodynamic model that uses the ability of oxalate to scavenge Ca2+ ion from the soil solution. The model predicts the increased solubility of Ca-apatite when oxalate is present in both the calcite-apatite (calcareous) system and in the exchangeable Ca-apatite (noncalcareous) system. The result is a marked increase of soluble (available) P in solution relative to the situation where oxalate is absent. The model is formulated on conditions prevalent in semiarid soils and presents a possible mechanism by which phosphorus uptake of plants is enhanced by mycorrhizal infection.