Stone pine (Pinus pinea L.) has been widely introduced for afforestation in Mediterranean areas. Despite its wide distribution and its presence since ancient time, it is mostly considered as non-native to the Italian peninsula. Plantation of non-native species may have a strong impact on the soil microbial community and, consequently, on nutrient cycling and soil functions. The effect of stone pine on soil microbial community structure and biomass, as revealed by phospholipid fatty acid (PLFA) analysis and fungal biomass indicators, was investigated in two Mediterranean areas in south Italy, where the climax tree species was holm oak (Quercus ilex L.) and some patches were afforested with stone pine. We studied soils from two sites with different parent material, volcanic lava and limestone (calcareous soil). The soil pH range was wider in the calcareous than in the volcanic soils. At both sites, the soils under stone pine had lower pH and higher organic matter content than under holm oak. Microbial biomass was, on average, 1.3-1.4 fold higher in the soils under holm oak than under stone pine. The PLFA composition was different in soils under stone pine compared with holm oak, while the changes in PLEA composition induced by the different tree species were comparable at the two sites. The changes in the PLFA composition were significantly correlated to soil pH and relative concentrations of PLFA indicators (mol%) previously demonstrated to indicate pH effects were also correlated to pH. Thus, both in the volcanic and the calcareous soils, stone pine plantation affected soil microbial community structure and the mechanism for this change appeared to be soil pH changes. (C) Elsevier B.V. All rights reserved.