Microbial activity and functional diversity in Psamment soils in a forested coastal dune-swale system

The aim of the study was to examine soil microbial activity and functional diversity in different parts of coastal landscapes influenced by recurring saltwater intrusion in the Ravenna area (Italy). For this reason, seven profiles were selected in the San Vitale Pinewood, in low-lying interdune spot and next to dune crests and swales. Soils were classified as Typic Psammaquent, Typic Ustipsamment, Aquic Ustipsamment and Sodic Psammaquent. Chemical, physical and biochemical properties of soil horizons, such as microbial biomass metabolic quotient and enzyme activity, were determined to examine the effects of soil salinity and sodicity levels on microbial activity and functional diversity. The various soils and horizons could be split into distinct groups based on Differential Function Analysis of their properties. Cellulase, xylosidase and arylsulfatase showed a peak of their activity in surface horizons of sodic soils. α-glucosidase activity also was high in deeper horizons of those soils. Moreover, functional diversity, evaluated through calculation of Shannon's diversity index, was higher in the surface and deeper horizons of saline soils than non-saline soils. Conversely, soil with shallow water-table showed similar enzyme activity to soil located in the highest spots of the dune system. However, the highest values of specific activity (per unit of organic carbon) recorded in the deep horizons of the Typic Ustipsamment soil suggested more efficient hydrolytic activity of organic substrates due to oxygenation of soil. In conclusion, hydromorphic conditions in these soils influence the efficiency of organic substrate hydrolysis while soil salinity and sodicity increase both biochemical activity and functional diversity of microbial communities.