Living and dead soil organic matter under different land uses on a Mediterranean island

Soil under six different land uses on Pianosa Island, in the Mediterranean Sea, was characterized in terms of microbial activity and organic matter quality, in order to define relationships between living and dead organic matter. Biological measurements and chemical and spectroscopic (13C NMR and FTIR) investigation of the extracted soil organic matter provided clues to the effects of soil management on the reciprocal interactions between living and dead organic matter. In particular, the conversion from the original bushy maquis to other land uses, such as degraded thickets of holm oak, maquis-invaded groves of olive trees, stands of Aleppo pines and abandoned pastures, implied significant reduction of soil organic carbon (SOC) and its microbial fraction (MBC). Cropland, which is the land use with the greatest perturbation of soil, had the smallest SOC, MBC and soil respiration rate. Significant differences in extractable SOC among land uses occurred, both as total amount and as molecular mass distribution. The relatively good relationship between soil respiration and the extracted SOM-fraction of 2-50 kDa, expressed on a molecular mass basis, suggests that this size is strongly linked to heterotrophic organisms and that it could be representative of a transitory pool of C in soil.