Role of Phosphatase Enzymes in Soil

Phosphatases have been extensively studied in soil, as shown by some reviews (Ramirez-Martinez 1968; Speir and Ross 1978; Malcom 1983; Tabatabai 1994), because they catalyse the hydrolysis of ester–phosphate bonds, leading to the release of phosphate (P), which can be taken up by plants or microorganisms (Cosgrove 1967; Halstead and McKercher 1975; Quiquampoix and Mousain 2005). It has been shown that the activities of phosphatases (like those of many hydrolases) depend on several factors such as soil properties, soil organism interactions, plant cover, leachate inputs and the presence of inhibitors and activators (Speir and Ross 1978). Phosphatases are enzymes catalysing the hydrolysis of both esters and anhydrides of phosphoric acid (Schmidt and Laskowski 1961) and, according to the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology, they can be classified as phosphoric monoester hydrolases or phosphomonoesterases (EC 3.1.3), phosphoric diester hydrolases or phosphodiesterases (EC 3.1.4), triphosphoric monoester hydrolases (EC 3.1.5) and enzymes acting on phosphoryl-containing anhydrides (EC 3.6.1) and on P–N bonds (EC 3.9). Phosphatases can also be subdivided according to their regulation (e.g. calmodulin), the requirements of metal cations for their activity (e.g. Mg2þ and Ca2þ) and their sensitivity to various phosphatase inhibitors. Phosphomonoesterases include acid and alkaline phosphomonoesterase (which hydrolyse monoester bonds including mononucleotides and sugar phosphates), phosphoprotein phosphatases (which hydrolyse phosphoester bonds of phosphoserines, phosphothreonines or phosphotyrosines), phytases (EC 3.1.3.26 for 4-phytase and EC 3.1.3.8 for 3-phytase, which hydrolyse all six phosphate groups from inositol hexaphosphate) and nucleotidases. Acid and alkaline phosphomonoesterases do not hydrolyse phosphates of phytic