The spatial differences in arylsulfatase enzyme activity on hillslopes along a climatic transect

Abstract

The research was conducted in Israel at 4 sites located along a south-north transect, along which climatic conditions range from arid in the south, through semi-arid, and Mediterranean, to humid Mediterranean in the north. At each site soil samples were collected in summer, winter, and spring over a 2-year period, from 3 microenvironments, from depths of 0–20 and 50–100 mm. The selected microenvironments at the arid, semi-arid, and Mediterranean sites were ‘under shrub’, ‘between shrubs’, and ‘under rock fragments’; those at the humid Mediterranean site were ‘under shrub’, ‘between shrubs’, and ‘under tree’. Intracellular and extracellular arylsulfatase enzyme activities, and some soil properties, were examined. The research aims were: (1) to analyse the relationship between arylsulfatase enzyme activity and some soil properties; (2) to analyse the effects of soil components (local factor) and climatic conditions (regional factor) on arylsulfatase enzyme activity. At both arid sites the organic carbon content, which had a positive effect on arylsulfatase activity, was much higher under shrubs and somewhat higher under rock fragments than between shrubs. At the semi-arid site this was also true of the moisture content. However, at the arid site high soil salinity and dryness limited the enzyme activity, especially the intracellular activity, under shrubs and rock fragments, respectively. In contrast, at the semi-arid site the organic matter was the main limiting factor of enzyme activity. Thus, the intracellular and extracellular activities of the enzyme were considerably higher under shrubs, and somewhat higher under rock fragments, than between shrubs. With increasing rainfall amount towards the Mediterranean sites the enzyme activity increased sharply and the differences between the under shrub, under rock fragment, and between shrubs microenvironments decreased sharply, mainly as a result of the reduction in the spatial variations in organic carbon. At the humid Mediterranean site enzyme activity under trees was considerably higher than that in other microenvironments, and this was expressed in the more suitable environmental conditions under trees, i.e. higher content of organic carbon, moisture, and aggregates.