Acid and alkaline phosphatase dynamics and their relationship to soil microclimate in a semiarid woodland

The seasonal dynamics of acid and alkaline phosphatase activity (mu g p-nit rophenol released g(-1) soil h(-1)), soil water potential and temperature, and the relationship of phosphatase activity to plant and soil microbial pr ocesses underneath Juniperus monosperma canopies and Hilaria jamesii-domina ted intercanopy areas were studied in a northern Arizona pinyon-juniper eco system. Alkaline phosphatase activity was significantly higher in soils und er junipers (126.5 +/- 3.9 mu g p-nitrophenol g(-1) soil h(-1)) than in int ercanopy soils (106.6 +/- 4.0 mu g p-nitrophenol g(-1) soil h(-1)), and sig nificantly exceeded acid phosphatase activity by a factor of 6, Seasonal hi gh phosphatase activities were up to 2.4 times greater than seasonal lows. Activities were maximal in summer and winter. Juniper soils were cooler tha n intercanopy soils except during the coldest months of the year, when they were up to 2.7 degrees C warmer. Intercanopy soils were up to 6.2 degrees C warmer than juniper soils, and had the highest (30.0 +/- 0.3 degrees C) a nd the lowest average temperatures (2.3 +/- 0.2 degrees C). Soil microclima te explained as much as 20% of the variation in acid and alkaline phosphata se, Temperature and water potential together were better predictors of phos phatase activity than either one alone. The soil water potential class -0.1 MPa greater than or equal to psi > -0.5 MPa was the most frequent best pre dictor of phosphatase activity, especially alkaline phosphatase. The winter peak in alkaline phosphatase activity is attributed to a buildup of phosph atase released into the soil from dying soil organisms, and the desorption and reactivation of previously accumulated phosphatase. (C) 2000 Elsevier S cience Ltd. All rights reserved.