Acid and Alkaline Phosphatase Dynamics in Soils of a Pifton-Juniper Woodland

-Plant roots and soil organisms increase phosphorus availability by releasing acid and alkaline phosphatase. Organic phosphorus compounds are hydrolysed into plant-available forms through the action of these enzymes. Phosphatase is of particular importance under conditions of low phosphorus availability which is commonly found in pinon-juniper soils. Acid and alkaline phosphatase activities (mg p-nitrophenol released g-1 soil h-1) were studied at two research sites in northern Arizona. At monthly intervals, soil samples were collected underneath Juniperus monosperma canopies and in interspace areas dominated by Hilaria jamesii. In both juniper and interspace soils, alkaline phosphatase activities were significantly higher than acid phosphatase activities. Alkaline phosphatase activity ranged from 57.3 to 167.2 fl9 p-nitrophenol g-1 soil h(1 and was similar to values reported for acid farmfield and grassland soils. Acid phosphatase activity varied between 9.3 and 29.5 mg p-nitrophenol g-1 soil h -1 and corresponded to values in Juniperus occidentalis and a range of western coniferous forest soils. The results indicate that soil microbes are the dominant producers of phosphatase in the studied pinon-juniper soils.