ARS | Publication request: Quantifying Bioactive P Pools in Fertilized and Manure-Amended Soils by Purified Phytic-Acid High Affinity Aspergillus phosphohydrolases

Submitted to: Eurosoil Congress
Publication Type: Abstract Only
Publication Acceptance Date: August 25, 2008
Publication Date: August 25, 2008
Citation: Dao, T.H., Hoang, K.Q. 2008. Quantifying Bioactive P Pools in Fertilized and Manure-Amended Soils by Purified Phytic-Acid High Affinity Aspergillus phosphohydrolases. EuroSoil2008 Book of Abstracts, No. P422:283.

Technical Abstract: In areas of intensive animal agriculture, repeated land application of manure resulted in elevated soil concentrations of inorganic and organic phosphorus (P) myo-Inositol hexaphosphate, lower phosphomonoesters are the most abundant organic P compounds. Such P-enriched soils are potential pollution sources, increasing risks of impairment to water quality of freshwater systems. Extracellular phosphohydrolases have been used to characterize organic P because they hydrolyze and release phosphate from P-containing organic compounds. As current enzymatic methods have been hampered by low recovery of soil P, we developed a mild in situ enzymatic method to quantify bioactive P in environmental samples such as manure, soil, water, and sediments. Induction and culture of five Aspergillus strains were conducted to develop a source of high-affinity phosphohydrolases. Differences existed in strains’ adaptability to fermentation medium as there was a wide range of phytate-degrading activity. Phosphohydrolases from A. ficuum had highest activity when the strain was cultured on a primarily chemical medium, exhibiting phytic acid-degrading potential equivalent to that of commercial preparations. Purified phosphohydrolases effectively quantified bioactive P pools in samples of fertilized and manure-amended soil planted to soybean [Glycine max (L.) Merr.]. Within-season changes in inorganic P pools and P uptake showed that the simple equilibration of soil with a dilute solution of polycarboxylate ligand performed equally well or exceeds the extraction efficiency of a strong acid Mehlich 3 extractant. Organic P species were similarly solubilized and dephosphorylated, yielding an additional enzyme-labile soil P fraction. Therefore, extracellular phosphohydrolases are effective sensors for environmental organic P and have an important role in assessing P internal dynamics in soils, nutrient bioavailability, and the effects of crop management in mitigating risks of P emissions to the environment.