Temporal and spatial variability of soil chemical and biological variables in a Mediterranean shrubland

The aim of this study was to analyze the effect of seasonality and of different plant species on soil microbial biomass and activity as well as on the availability of C, N, and P in a Mediterranean shrubland. We compared the temporal and the spatial variability of soil chemical and biological variables recorded in the soil underneath the canopy of three evergreen sclerophyllous (Quercus coccifera, Juniperus oxycedrus, and Erica sp.) and two seasonally dimorphic shrubs (Globularia alypurn and Thymus capitatus) and in the grass-covered area between them. Although the effects of sampling period and plant species were significant for all of the studied variables, seasonality dominates over heterogeneity induced by plant species. All variables displayed high values in February except for inorganic P, which was higher in June. Microbial biomass N, ergosterol, and NO3- exhibited the lowest values in June; N-mineralization rate and soil respiration in September; while C-mineralization rate was low at both times. Plant life form (shrubs or grasses; evergreen sclerophyllous or seasonal dimorphic shrubs) is a factor inducing differences in soil biochemical processes. Soil samples collected under the dimorphic species share common properties, whereas distinct soil environments were recorded under different evergreen species. (C) 2004 Elsevier B.V. All rights reserved.