Biochars reduce infection rates of the root-lesion nematode Pratylenchus penetrans and associated biomass loss in carrot Carmen George a, b , Josef Kohler a, b , Matthias C. Rillig a, b, * a Freie Universit€ at Berlin, Institut für Biologie, Plant Ecology, Altensteinstr. 6, D-14195 Berlin, Germany b Berlin-Brandenburg Institute of Advanced Biodiversity Research (BBIB), D-14195 Berlin, Germany article info Article history: Received 9 July 2015 Received in revised form 29 November 2015 Accepted 1 December 2015 Available online 22 December 2015 Keywords: Biochar Plant parasitic nematodes Pratylenchus penetrans Systemic resistance Systemic acquired resistance Induced systemic resistance abstract Biochars, in addition to carbon sequestration, soil amelioration and improvement of plant performance, can measurably reduce disease severity of different pathogen types and even induce system wide de- fense responses in host plants. The aim of this study was to further investigate if biochars can provide resistance-enhancing effects to host plants faced with plant parasitic nematodes. We asked if these carbonized materials, as a result, may hold the potential to be used as an effective supplement for chemical nematicides. Four different biochars and zeolite (5% v/v) were tested on a carrot (Daucus carota) and root-lesion nematode (Pratylenchus penetrans) pathogen system. Plant biomass, nematode abun- dances in soil and root tissue (infection rate), as well as plant-nutrient status were quantified. P. penetrans caused decreased shoot- and fine root biomass in infected plants. All applied materials, except for the pine wood biochar, significantly reduced tap root infection rates of P. penetrans by approximately 80% and spelt husk biochar actually reduced infection rates by more than 96%. Infected plants of these treatments produced two to four times more plant biomass than infected plants of the non-material application treatment. It turned out that biochars produced from different feedstocks affected nematode infection rates and host plant biomasses quite differently. Induced resistance is a possible explanation for the highly reduced infection rates, as direct toxic effects of the biochar and effects of altered pH, water holding capacity, soil structure and plant nutrient status could be largely excluded. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction During the past decade, the production of carbonized materials and the subsequent application to soils has increasingly become a subject of scientific and agricultural interest (Lehmann and Joseph, 2015). In general, carbonized materials are a byproduct of a thermal decomposition process of biomass, which is referred to as pyrolysis. In contrast to the process of burning, pyrolysis of biomass takes place under limited or no oxygen supply, resulting in gaseous, liquid and solid products. As oxidation processes are almost non- existent or highly reduced, the resulting solid byproduct is char- acterized by a very high carbon content (char). This process of “carbon enrichment” has been used by mankind since ancient times for turning wood into charcoal (Antal and Gronli, 2003) and nowadays is of increasing interest in terms of emerging environ- mental challenges of our time. The application of carbonized materials to soil could provide the opportunity to sustainably improve soil health, nutrient retention and carbon storage and thereby help to face present problems of soil depletion and productivity, as well as problems of rising at- mospheric greenhouse gas concentrations. In order to be able to differentiate these soil-applied charcoals from other pyrolysis derived materials, which are usually produced in terms of energy production, the term biochar was introduced (Lehmann and Joseph, 2015). The application of biochar to soil has often been reported to have positive effects on plant growth and significantly increase crop yields (Lehmann et al., 2003; Steiner et al., 2007; Major et al., 2010) but also negligible to adverse ef- fects are common results in biochar experiments (Jefferey et al., 2011; Spokas et al., 2012). These contrary results are not a big surprise when taking into account that biochars differ significantly in their physicochemical and biological properties, depending on * Corresponding author. Institut für Biologie, Dahlem Center of Plant Sciences e Plant Ecology, Altensteinstr. 6, D-14195 Berlin, Germany. Tel.: þ49 30 838 53165; fax: þ49 30 838 53886. E-mail address: matthias.rillig@fu-berlin.de (M.C. Rillig). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio http://dx.doi.org/10.1016/j.soilbio.2015.12.003 0038-0717/© 2015 Elsevier Ltd. All rights reserved. Soil Biology & Biochemistry 95 (2016) 11e18