Quantification of pyrophosphate in soil solution by pyrophosphatase hydrolysis

A commercial pyrophosphatase from Saccharomyces cerevisiae selectively hydrolyzed sodium pyrophosphate, but showed no significant activity towards a range of other organic and condensed inorganic phosphorus compounds. Pyrophosphate determined by pyrophosphatase hydrolysis accounted for 38 12% (mean standard error of 19 sites) of the non-reactive phosphorus in soil solution obtained by centrifugation from a series of lowland tropical rain forest soils. Pyrophosphate concentrations were up to 89 mg P l 1 and correlated positively with microbial phosphorus, soil solution pH, and native phosphomonoesterase activity in soil solution, but not with total soil pyrophosphate determined by NaOH eEDTA extraction and solution 31P NMR spectroscopy. In summary, we identify pyrophosphate as a major constituent of soil solution phosphorus in lowland tropical rain forests, and demonstrate that a commercial pyrophosphatase can be used as a selective tool to quantify trace concentrations of pyrophosphate in soil solution. 2014 Elsevier Ltd. All rights reserved. Pyrophosphate is ubiquitous in soils, where it appears to originate mainly from soil fungi (Rasmussen et al., 2000; Makarov et al., 2005; Bünemann et al., 2008). However, the role of pyrophosphate in the nutrition of plants remains poorly understood, due in part to the difficulty in its quantification at low concentrations in soil solution. Ion chromatography was used to assess the fate of pyrophosphate fertilizer added to soils (e.g., McBeath et al., 2007), while pyrophosphate can be quantified in alkaline soil extracts by solution 31P NMR spectroscopy (e.g., Turner et al., 2003). However, the latter procedure is inappropriate for analysis of soil solution due to its relative insensitivity. Several studies have used phosphatase enzymes to detect phosphorus compounds in soil solution or soil water extracts (e.g. Shand and Smith, 1997; Hayes et al., 2000; Turner et al., 2002). Phosphatases added to soil solution or extracts catalyze the hydrolysis of specific functional organic phosphorus groups, allowing detection of the released orthophosphate by routine colorimetry. Phosphatase hydrolysis procedures are sufficiently sensitive to quantify trace concentrations of organic phosphates in solution, but established protocols have not identified pyrophosphate separately from simple phosphomonoesters (reviewed in