Acid Phosphomonoesterase Activity in Floodplain Forest Soils

The 4-nitrophenyl phosphate method for acid phosphomonoesterase (EC 3.1.3.2; acid orthophosphoric monoester phosphohydrolase) determination was slightly modified to increase the sensitivity and the stability of the 4-nitrophenol coloured complex in samples rich in humic substances and easily soluble organic compounds. Based on an approach used for mycorrhizal roots, the new analytical protocol was tested on samples taken from a single forest site with a large variation in soil types. Distinctive properties of forest soils and the accuracy/repeatability of the optimised technique were considered in the selection of the most appropriate analytical steps. Finally, the acid phosphomonoesterase activity was expressed in μg of 4-nitrophenol/g fresh soil recalculated dry matter/h released after hydrolysis of 4-nitrophenyl phosphate in sodium tetraborate/succinic acid buffer at pH 4.8. The modified method proposed was statistically compared with other procedures and the results obtained were found to give merit to these slight modifications. The rationale behind the slight modifications and their comparative significance was reported. Due to high soil complexity, it is suggested that a single laboratory measurement of chemical and biochemical properties is of limited application with forest soil and can be only one component of a broadly focused ecological analysis.