Temporal dynamics in arylsulfatase enzyme activity in various microenvironments along a climatic transect in Israel

Abstract

The research was conducted in Israel, at three sites located along a north–south axis, characterized by increasing annual rainfall, from 310 mm at site LAV in the south through 600 mm at site MAT, to 800 mm at site EIN in the north. Soil samples were collected in summer, winter and spring over a 2-year period (September 2001–April 2003) from two layers (0–2 cm and 5–10 cm) in three dominant microenvironments. At LAV and MAT the selected microenvironments were “under shrub” (US), “between shrubs” (BS) and “under rock fragments” (UR). At EIN the selected microenvironments were US, BS and “under tree” (UT). The temporal variations in the intracellular and extracellular activities of arylsulfatase, an enzyme that hydrolyzes the sulfate ester in soil, were examined along this transect. The temporal variations in the enzyme activity varied considerably among the sites. At the Mediterranean sites the intracellular activity exhibited a clear seasonal variations in both years, with relatively low values in the dry summer and relatively high values in the rainy winter and spring. At the semi-arid site seasonal variations were less clear. Whereas at sites LAV and MAT the intracellular enzyme activity did not change, or even increased, as the annual rainfall increased, at site EIN the activity decreased sharply. The temporal variations in the extracellular enzyme activity at site LAV followed those of the intracellular activity, whereas at both MAT and EIN the temporal variations in extracellular enzyme were not clear. Nevertheless, it was demonstrated that the extracellular activity reduced percentage of the total enzyme activity as the seasons progressed from summer through winter and spring, in contrast to the temporal variations in the intracellular activity. This indicated that at sites MAT and EIN the production of extracellular enzymes by microorganisms changed considerably among seasons in response to the large seasonal changes in the availability of the organic matter. In addition, at sites LAV and MAT the temporal variations in the enzyme activity differed among the microenvironments as a result of their differing soil water regimes. At the semi-arid site, LAV, the increase in enzyme activity with increasing annual rainfall was most significant in the ‘humid’ microenvironment, US. At the Mediterranean site, MAT, it was most significant in the ‘dry’ microenvironment, BS. In contrast to sites LAV and MAT, at site EIN, the changes in enzyme activity between years were similar in all the microenvironments, which imply that at this site the changes in enzyme activity were affected by regional factors.