Changes in microbial community structure and functioning of a degraded soil due to the use of anaerobic digestate derived composts and rosemary plants

Since most of the soil processes are microbial mediated, soil microorganisms are central to the soil ecological functioning, providing several regulation ecosystem services. Microbial activity and soil fertility are closely related and the soil microorganisms adapts quickly to environmental constrains by adjusting their biomass, activity rates and community composition. Microbial structure and its biochemical properties can represent sensitive indicators of soil quality. We studied the changes in the structure and functioning of the microbial community in a degraded agricultural soil after the incorporation of two composts, obtained from cattle manure or pig slurry anaerobic digestate, and the use of rosemary plants for restoring soil quality. The composts were applied at low or high doses on soil samples (30 or 60 t ha-1 , respectively), which were maintained in microcosms for 6 months. Some soil microcosms were treated with inorganic fertiliser and other non-treated soils were used as microbiological controls. Rosemary plants, used both for their ability to grow in semi-arid regions and for the capacity of their root system to protect soil from erosion, were planted in half of the entire microcosm set up. At different times (0-180 days) microbial abundance, cell viability and dehydrogenase activity were measured in the different experimental treatments. Total and water-soluble soil organic carbon and nitrogen contents were assessed at 0 and 180 days. With an increase in carbon and nitrogen soil content, an increase in microbial abundance was also observed in the presence of both composts. However, microbial activity was significantly influenced by rosemary presence, without considering the allochthonous carbon and nitrogen input. Moreover, microbial community structure and diversity was also assessed by Fluorescence In Situ Hybridization in the different treatments. The highest values for microbial community biodiversity were found in the copresence of the rosemary plant and at low concentration of both composts. The overall results suggest that the use of composts together with plant species suited to Mediterranean areas seems to be an appropriate strategy for restoring soil quality and the ecosystem services provided by microorganisms.