Microbial activity in soils under fast-growing Paulownia ( Paulownia elongata x fortunei) plantations in Mediterranean areas

► We evaluate the effects of fast-growing paulownia plantations, Aleppo pine forestations, maize crops and soils without human interference on the chemical, physical and microbiological soil properties. ► Aleppo pine forestations and control plots presented higher enzymatic activities and soil respiration than agricultural uses or paulownia plantations. ► Soil aeration or heavy metals found in the Paulownia plantations reduce the soil respiration and enzymatic activity levels. ► Enzymes and soil respiration might be useful as early indicators of biological changes. Most agroforestry projects and plantations for biomass production may affect soil properties and status. The objective of this work was to know the effects of paulownia ( Paulownia ssp.) plantation on the chemical, physical and microbiological properties of soils in Mediterranean agricultural areas. Aleppo pine ( Pinus halepensis L.) forestations, maize ( Zea mays L.) crops and soils without human interference were also selected in the same area in order to compare results obtained. Paulownia plantations and maize crops showed higher values of organic matter content, total N, total organic carbon and heavy metals (Cu, Cr, Pb, Ni and Zn). However, Aleppo pine forestations and control plots presented higher enzymatic activities (phosphatase, β-glucosidase and dehydrogenase) and soil respiration than agricultural uses or paulownia plantations. Thus, the ploughing operations with the consequent increased soil aeration, fertilization and cropping practices, as well as the vegetation management and composition negatively influence microbial populations and enzyme activity. Paulownia plantation should avoid the use of machinery and fertilization, which incorporate heavy metals into the soil or increases soil aeration, reducing the soil respiration and enzymatic activity levels. Moreover, enzymes and soil respiration might be useful as early indicators of biological changes.