Effect of plant cover decline on chemical and microbiological parameters under Mediterranean climate

The uses of many of the soils of Central Spain have changed and these changes have led frequently to the decline of natural plant cover. In this paper we report on the organic matter fractions and the microbial activity of soils developed from different substrates (limestone and granites) in relation to plant cover decline. Specific indicators of microbial activity (microbial biomass carbon (MBC), basal respiration, and some oxidoreductase and hydrolase activities) were measured. These indicators decreased in value in both limestone and acid soils where plant cover had declined (from climax, tree forest, to low bush); a similar effect was observed in the labile organic matter fractions (water soluble carbon (WSC), water soluble carbohydrates and polyphenolic compounds). For some measures of microbiological activity (e.g. MBC and soil respiration) the differences in acid soils were lower than in limestone soils. For example, MBC values in limestone soils ranged from 1426 ngC g−1 in tree forest to 498 ngC g−1 in low bush; while in acid soils, these values ranged from 428 ngC g−1 in tree forest to 265 ngC g−1 in low bush. Acid soils, unlike the limestone soils, showed no relationship between plant cover decline and hydrolase activities related to the N cycle (urease and protease). In general, soil microbial activity was negatively affected by plant cover degradation.