Microbiological indicators to evaluate ecosystem soil quality and its changes in diversity and functioning.

Soil quality represents an integral value of the compositional structures and natural functions of soil in relation to soil use and environmental conditions on site. Among the main soil components, different organisms and in particular microorganisms play a key role in ecologically biogeochemical processes. In this way, soil microorganisms contribute to the maintenance of the matter and energy transfer in terrestrial environments. Under anthropogenic stress conditions such as intensive agriculture and diffusion of pollutants, biochemical activities of soil microorganisms can be differently affected. Several microbiologically-related parameters contribute to provide an ecological evaluation of soil state therefore, they can be considered as indicators of soil quality. In this regard, we report some preliminary results of a Research Project dealing with three sites, located close to Taranto City, in the South of Apulia Region (Italy), affected by land degradation processes such as soil organic matter decline and/or organic (PCB) and inorganic contamination. Soil samples were collected and both chemical and microbial analyses were performed in order to evaluate the quality of the soils and to compare the three sites. For this purpose, the main physico-chemical soil characteristics (organic carbon, available phosphorous, total nitrogen, carbonate and water content, texture and pH) were determined. Moreover, some samples have been analysed by GC-MS and ICP-MS in order to identify organic (PCB) and inorganic (e.g. Pb, Se, Sn, Zn) contaminants, respectively. Finally, the structure and functioning of the bacterial community was studied by evaluating the bacterial abundance (DAPI counts), the cell viability (Live/Dead method), the dehydrogenase activity (DHA), and the Microbial Community Composition by Fluorescence In Situ Hybridization (FISH). The overall results showed that the bacterial structure and functioning were affected in different way by the organic carbon availability and contaminant occurrence (organic or inorganic compounds), showing how land degradation processes can affect ecosystem soil biodiversity and functioning.