Assessment of bioavailable organic phosphorus in tropical forest soils by organic acid extraction and phosphatase hydrolysis

A - Papers appearing in refereed journals

Darch, T., Blackwell, M. S. A., Chadwick, D., Haygarth, P. M., Hawkins, J. M. B. and Turner, B. L. 2016. Assessment of bioavailable organic phosphorus in tropical forest soils by organic acid extraction and phosphatase hydrolysis. Geoderma. 284 (15 December), pp. 93-102.

AuthorsDarch, T., Blackwell, M. S. A., Chadwick, D., Haygarth, P. M., Hawkins, J. M. B. and Turner, B. L.
Abstract

Soil organic phosphorus contributes to the nutrition of tropical trees, but is not accounted for in standard soil phosphorus tests. Plants and microbes can release organic anions to solubilize organic phosphorus from soil surfaces, and synthesize phosphatases to release inorganic phosphate from the solubilized compounds. We developed a procedure to estimate bioavailable organic phosphorus in tropical forest soils by simulating the secretion processes of organic acids and phosphatases. Five lowland tropical forest soils with contrasting properties (pH 4.4–6.1, total P 86–429 mg P kg− 1) were extracted with 2 mM citric acid (i.e., 10 μmol g− 1, approximating rhizosphere concentrations) adjusted to soil pH in a 4:1 solution to soil ratio for 1 h. Three phosphatase enzymes were then added to the soil extract to determine the forms of hydrolysable organic phosphorus. Total phosphorus extracted by the procedure ranged between 3.22 and 8.06 mg P kg− 1 (mean 5.55 ± 0.42 mg P kg− 1), of which on average three quarters was unreactive phosphorus (i.e., organic phosphorus plus inorganic polyphosphate). Of the enzyme-hydrolysable unreactive phosphorus, 28% was simple phosphomonoesters hydrolyzed by phosphomonoesterase from bovine intestinal mucosa, a further 18% was phosphodiesters hydrolyzed by a combination of nuclease from Penicillium citrinum and phosphomonoesterase, and the remaining 51% was hydrolyzed by a broad-spectrum phytase from wheat. We conclude that soil organic phosphorus can be solubilized and hydrolyzed by a combination of organic acids and phosphatase enzymes in lowland tropical forest soils, indicating that this pathway could make a significant contribution to biological phosphorus acquisition in tropical forests. Furthermore, we have developed a method that can be used to assess the bioavailability of this soil organic phosphorus.

Keywordscitric acid; organic acid; organic phosphorus; phosphatase hydrolysis; tropical; bioavailable
Year of Publication2016
JournalGeoderma
Journal citation284 (15 December), pp. 93-102
Digital Object Identifier (DOI)doi:10.1016/j.geoderma.2016.08.018
Open accessPublished as ‘gold’ (paid) open access
FunderBiotechnology and Biological Sciences Research Council
Funder project or codeSustainability
Exploiting root exudation of organic acids and phytases to enhance plant utilisation of soil phosphorus
Publisher's version
Output statusPublished
Publication dates
Online07 Sep 2016
Publication process dates
Accepted26 Aug 2016
Copyright licenseCC BY
ISSN0016-7061
PublisherElsevier Science Bv

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