Changes in microbial community structure and functioning of a semiarid soil due to the use of anaerobic digestate derived composts and rosemary plants Anna Barra Caracciolo a , Maria Angeles Bustamante b , Isabel Nogues c , Martina Di Lenola a , Maria Laura Luprano a , Paola Grenni a, ⁎ a Water Research Institute, National Research Council of Italy, Via Salaria km 29.300, Monterotondo, Rome Italy b Department of Agrochemistry and Environment, Miguel Hernandez University, EPS-Orihuela, ctra. Beniel km 3.2, 03312 Orihuela, Spain c Institute of Agro-Environmental and Forest Biology, National Research Council of Italy, Via Salaria km 29.300, Monterotondo Rome, Italy abstract article info Article history: Received 3 July 2014 Received in revised form 26 December 2014 Accepted 13 January 2015 Available online xxxx Keywords: Microbial activity and diversity Soil bacteria Rhizosphere Degraded soil Organic amendments Compost We studied the changes in structure and functioning of the microbial community in a degraded agricultural soil after the addition 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 added at low or high doses to soil samples (30 or 60 t ha -1 , respectively), which were kept 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 and dehydrogenase activity were measured in the various 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, a rise in microbial abundance was also observed in the presence of both composts. However, microbial activity was significantly influenced by the presence of rosemary, without considering the allochthonous carbon and nitrogen input. Microbial community structure and diversity were also assessed by Fluorescence In Situ Hybridization in the different treatments. The highest values for microbial community biodiversity were found in the co-presence of rosemary and at low concentrations 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. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The loss of organic matter and biodiversity are among the main threats to soil quality, as identified by the EU Soil Thematic Strategy COM 2006 (231) and in the Policy report on its implementation, COM 2012 (46). Soil Organic Matter (SOM) depletion and soil erosion are caused by inappropriate agricultural practices, clearing of vegetation, increased levels and frequency of drought or flooding and forest fires. It has been observed, for example, that land without vegetation can be eroded more than 120 times faster than land covered by vegetation, which can thus lose less than 0.1 tons of soil per ha year -1 (Turbé et al., 2010). The activity and diversity of soil microorganisms are directly affected by the reduction of SOM content, and indirectly by the reduction in plant diversity and productivity. Microbial commu- nities play a key role in organic matter decomposition (Lavelle and Spain, 2001; Chaudhry et al., 2012) and in biogeochemical cycles (Doran and Zeiss, 2000; Paul, 2007; Zhong et al., 2010) and enhance the efficiency of plant nutrient assimilation by promoting their growth and health (Gu et al., 2008; Güneş et al., 2014). Since most of the soil processes are microbially mediated, soil microorganisms are central to soil ecological functioning, providing several regulation ecosystem services (Millennium Ecosystem Assessment, 2005). Microbial activity and soil fertility are closely related and the soil microbiota adapts quick- ly to environmental constrains by adjusting its biomass, activity rates and community composition. Microbial structure and its functioning can represent accurate indicators of soil quality (Winding et al., 2005; Benedetti et al., 2006; Giacometti et al., 2013). Only recently has more attention been focused on the maintenance of the structural and func- tional diversity of soil bacterial communities and the ways in which they might respond to various natural or anthropogenic disturbances (Zhang and Xu, 2008; Bouasria et al., 2012). Geoderma 245–246 (2015) 89–97 ⁎ Corresponding author at: Water Research Institute, National Research Council of Italy, Via Salaria km 29.300, Monterotondo, Rome, Italy. E-mail address: grenni@irsa.cnr.it (P. Grenni). http://dx.doi.org/10.1016/j.geoderma.2015.01.021 0016-7061/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma