Enzymatic hydrolysis of soil organic phosphorus by immobilized phosphatases

Abstract

In order to estimate the role of phosphatases in maintaining the potential bioavailable P pool in soils, water and 0.4 M NaOH soil extracts were incubated with immobilized acid phosphatase, alkaline phosphatase, phospholipase and nuclease, separately, and in combinations. Immobilized nuclease at an optimum pH of 7.0 hydrolyzed the most soluble unreactive P (SUP) both in water and 0.4 M NaOH extracts. The combination of immobilized alkaline phosphatase and nuclease increased the hydrolysis of SUP at pH 7.0 by up to 61% in 0.4 M NaOH extracts relative to that due to immobilized nuclease alone. The combination of immobilized acid phosphatase and nuclease, however, did not increase the hydrolysis of SUP in either extract relative to that due to immobilized nuclease alone. Immobilized alkaline phosphatase and phospholipase increased the hydrolysis of SUP at pH 7.0 by up to 62% in 0.4 M NaOH extracts relative to that due to immobilized phospholipase alone. Similarly, immobilized acid phosphatase and phospholipase increased the hydrolysis of SUP at pH 7.0 by up to 49% in 0.4 M NaOH extracts relative to that due to immobilized phospholipase alone. The similarities in the optimum pH of indigenous phosphatases in soils and the immobilized phosphatases used in this study, immobilized on positively charged supports, suggests that indigenous phosphatases could be immobilized on positively charged surfaces in soils.