Figure 1.

Soil extracellular activities of urease, protease, β-glucosidase, and acid and alkaline phosphatases expressed in mg substrate released g⁻¹ soil dry weight h⁻¹ in Mediterranean soils compared with temperate and tropical soils. The reports have analyzed urease activity by the Kandeler and Gerber (1988) method or by comparable methods such as that of Tabatabai and Bremner (1969), protease activity by the Ladd and Butler (1972) method, β-glucosidase activity by the Eivazi and Tabatabai (1988) or related methods (Dick et al. 1996), and acid and alkaline phosphatase activities by the Tabatabai and Bremner (1969) and comparable methods (Tabatabai 1994). The values presented are those of controls when diverse treatments were applied to the studied soils and of the annual mean when several measurements were conducted throughout the year. The number of studies reviewed, by biome and enzyme, are depicted above the bars. The bars indicate mean (+ S.E.). For detailed information, see Table S1 in the supplementary material.