Components of organic phosphorus in soil extracts that are hydrolysed by phytase and acid phosphatase |
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| Authors: | J E Hayes A E Richardson R J Simpson |
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| Institution: | (1) CSIRO Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia@e-mail: alan.richardson@pi.csiro.au@Tel.: +61-2-62465189@Fax: +61-2-62465000, AU;(2) Division of Biochemistry and Molecular Biology, Australian National University, Canberra ACT 0200, Australia, AU |
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| Abstract: | Extracts were prepared from soil using water, 50 mM citric acid (pH ∼2.3) or 0.5 M NaHCO3 (pH 8.5), and were incubated with excess phytase from Aspergillus niger to determine the amounts of labile P. Two A. niger phytase preparations were used: (1) a purified form which exhibited a narrow substrate specificity and high specific activity
against phytate; and (2) a commercial preparation (Sigma) with activity against a broad range of P compounds. A comparatively
large proportion (up to 79%, or 5.7 μg g–1 soil) of the organic P (Po) extracted with citric acid was hydrolysed by the commercial phytase, while between 28% and 40% (up to 3.1 μg g–1 soil) was hydrolysed using purified phytase. By comparison, only small quantities of the Po in water and NaHCO3 soil extracts were enzyme labile. While extractable Po was increased both with increasing concentrations of citric acid (up to 50 mM) and increasing pH (pH 2.3–6.0), enzyme-labile
P increased only with citric acid concentration. The labile component of Po in citric acid extracts from soils with contrasting fertiliser histories indicated that enzyme-labile Po is a relatively large soil P pool and is potentially an important source of P for plants.
Received: 29 October 1999 |
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| Keywords: | Citric acid Organic phosphorus Phosphatase Phytase Soil phytate |
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