Comparison of absolute biochemical parameters of undisturbed soils in Mediterranean environments (NE Spain) with corresponding parameters relative to soil organic carbon

- Relative parameters were the most useful to detect the main differences between soils.
- The obtained groups of soils corresponded with the soil physicochemical properties.
- Soils with lower organic matter had a higher capacity to maintain microbial activity.
- Organic matter labile fraction content and pH values allowed us to group the soils.

The study of soil quality requires the establishment of quality standards. To this end, several authors have highlighted the need to create databases of quality indicators, such as biochemical properties, for different types of undisturbed soils under various climates and to establish standardised methodologies for their development. In Spain, studies of the quality of native soils were initiated > 15 years ago by several groups of authors from differing locations, but little is known regarding the biochemical characteristics of native soils in Catalonia (NE Spain). This study examines representative, minimally disturbed soils from Catalonia with a wide range of organic carbon contents. We examined the total and extractable organic carbon contents, total and extractable carbohydrates contents, enzyme activities (β-glucosidase, β-galactosidase, BAA-protease and urease), microbial biomass carbon and basal respiration of ten selected soils. Statistical analyses were applied to absolute values (i.e., per g of soil) and relative values (i.e., per g of soil organic carbon). The aim of this work was to determine the dependence of these properties on the organic matter content and the suitability of the relative values as soil quality indicators. The biochemical and microbiological parameter values of the native Catalan soils showed unusually wide ranges, although all of the values were similar to those already published for native soils in other Mediterranean climate areas. Overall, the sampled soils could be distinguished by their contents of organic carbon and total and extractable carbohydrates, rather than by their enzyme activities or microbiological variables; nevertheless, when the relative values were considered, the soils could be distinguished by their specific enzyme activities, particularly that of β-glucosidase, and by the labile proportion of organic matter. With the exception of the total carbohydrates/C ratio, the biochemical and microbiological parameters, expressed as functions of soil organic carbon content, were useful in distinguishing groups of native soils according to field observations and soil physicochemical properties.