Gasification biochar has limited effects on functional and structural diversity of soil microbial communities in a temperate agroecosystem Valentina Imparato a , Veronika Hansen b , Susana S. Santos a , Tue Kjærgaard Nielsen a , Laura Giagnoni d , Henrik Hauggaard-Nielsen c , Anders Johansen a , Giancarlo Renella d , Anne Winding a, * a Department of Environmental Science, Aarhus University, Roskilde, Denmark b Department of Plant & Environmental Sciences, University of Copenhagen, Denmark c Department of People and Technology, Roskilde University, Denmark d Department of Agrifood Production and Environmental, University of Florence, Italy article info Article history: Received 2 February 2016 Received in revised form 20 April 2016 Accepted 8 May 2016 Available online 17 May 2016 Keywords: Carbon sequestration Toxicity test Acidobacteria Microbial activity MicroResp 16S Illumina sequencing abstract Biochar may enhance soil fertility and carbon (C) sequestration but there is still a lack of comprehensive understanding of its effects on soil microbial communities and functioning. This study tested the dif- ferential effects of two doses (6e8 and 0.8e1.4 t ha 1 for High and Low doses, respectively) of wheat straw gasification biochar (GBC) and fresh straw incorporated as soil amendments into an agricultural field in Denmark. Soils were analysed three months after the amendments for pH, total organic matter, microbial biomass (ATP), ten enzymatic activities, catabolic potential by substrate-induced respiration (MicroResp™), soil toxicity test (BioTox™) and bacterial community structure (Illumina 16S rRNA gene sequencing). No significant effect of biochar treatment was observed regarding ATP content, catabolic community profiles and soil toxicity. The higher dose of GBC increased phenol oxidase activity and soil pH, and decreased the cellulase activity. No major effect of high dose GBC was observed on the soil community diversity, and only minor effect on the community composition, with an increase in the relative abundance of a single OTU associated with Acidobacteria_Gp16. Addition of low dose of GBC caused an increase in the relative abundance of the rare members in the microbial communities thus increasing the diversity of soil microorganisms. A comparable effect was observed with the addition of fresh straw. Overall, our results indicated that GBC as soil amendment had a limited effect on the functional and structural diversity of soil microbial communities in a Danish temperate agroecosystem. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Incorporation of charred plant residues into agricultural soils has multiple positive effects on the environment by obtaining renewable energy during biochar production, improving the uti- lisation of a variety of low-value and challenging biomass fuels from different sectors of society, returning nutrients to the field, and thus closing the nutrient loops in agroecosystems (Lehmann, 2007). Biochar is, by definition, charred organic matter that can be applied to soil in a deliberate manner with the intention of improving soil properties (Lehmann and Joseph, 2009). There is a growing interest in biochar application to soil as a strategy to improve fertility and mitigate CO 2 emission to the atmosphere by carbon (C) sequestration (Cernansky, 2015; Lehmann and Joseph, 2009). The effects of charred matters on soil fertility depend on their chemical properties, their impact on the soil microbiota and key soil functions caused by alkalinisation, release of trace elements and volatile organic compounds, (VOCs) (Deenik et al., 2010; Graber et al., 2010; Spokas et al., 2011; Sun et al., 2015), and by alteration of the nutrient availability. In biochar-amended soils, nutrient avail- ability depends on level of soil alkalinity that enhances the release of nutrients as dissolved organic C (DOC), nitrogen (N), and phos- phorous (P) and their complexation with the reactive functional groups onto the surface of the char particles (Joseph et al., 2015; * Corresponding author. E-mail addresses: vim@envs.au.dk (V. Imparato), veha@plen.ku.dk (V. Hansen), suss@envs.au.dk (S.S. Santos), tkn@envs.au.dk (T.K. Nielsen), laura.giagnoni@unifi. it (L. Giagnoni), hnie@ruc.dk (H. Hauggaard-Nielsen), ajo@envs.au.dk (A. Johansen), giancarlo.renella@unifi.it (G. Renella), aw@envs.au.dk (A. Winding). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio http://dx.doi.org/10.1016/j.soilbio.2016.05.004 0038-0717/© 2016 Elsevier Ltd. All rights reserved. Soil Biology & Biochemistry 99 (2016) 128e136