Pedobiologia 56 (2013) 219–224 Contents lists available at ScienceDirect Pedobiologia - International Journal of Soil Biology jo ur nal ho mepage: www.elsevier.de/pedobi Earthworms can modify effects of hydrochar on growth of Plantago lanceolata and performance of arbuscular mycorrhizal fungi Mohamed Salem a , Josef Kohler a , Susanne Wurst a , Matthias C. Rillig a,b,∗ a Freie Universität 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 a r t i c l e i n f o Article history: Received 12 July 2013 Received in revised form 9 August 2013 Accepted 29 August 2013 Keywords: Hydrochar Hydrothermal carbonization Earthworms AMF Plantago lanceolata Biochar a b s t r a c t Hydrothermal carbonization (HTC) is a method to produce carbonized material at relatively low temper- atures (180–250 ◦ C) under pressure and aqueous conditions. The product is called hydrochar and can be used as a soil amendment. However, applied in high dosages it may have detrimental effects on plants or soil biota. The potential impact of hydrochar amendment on beneficial soil organisms such as arbuscular mycorrhizal fungi (AMF) and earthworms and their interactions are not well understood. The goal of the present study was to determine effects of hydrochar on plant growth and soil biota and to evaluate interactions of earthworms and hydrochar on plant and AMF performance and to identify underlying mechanisms. In a greenhouse experiment, we investigated the effect of hydrochar at different addition rates (control, 1% and 10%, v/v) with or without the earthworm Aporrectodea caliginosa on the growth of Plantago lanceolata L. and the performance of its AMF. We observed a positive interaction between earthworms and 10% hydrochar on shoot and root biomass: added as a single treatment hydrochar had a negative effect on plant growth at this dosage, but plant biomass increased significantly when hydrochar was added together with earthworms. Root colonization by AMF increased significantly with increas- ing concentration of hydrochar, but was not affected by earthworms. Contrastingly, extraradical hyphal length of AMF was reduced by earthworms, but not affected by hydrochar. Thus, hydrochar and earth- worms affected the performance of AMF, albeit of different AMF structures and in different directions. Our results indicate that earthworms may play an important role in alleviating the negative impacts of high dosages of hydrochar on plant growth; such interactions should move into focus of future research on potential effects of HTC materials. © 2013 Elsevier GmbH. All rights reserved. Introduction When searching for solutions to mitigate the greenhouse effect, carbon storage in soil can be a potential way to curtail the increas- ing concentration of CO 2 in the atmosphere. One possible solution is soil amendment with carbonized material. Carbonized materials are produced by thermal decomposition of organic material under limited oxygen supply (Lehmann and Joseph, 2009) and are char- acterized by a high C content with aromatic compounds which are relatively stable in soil (Noguera et al., 2010). The product of this pyrolysis is called biochar, which is obtained by heating organic materials (up to 700 ◦ C) in a closed system (Lehmann and Joseph, 2009). Hydrothermal carbonization (HTC) is a recently rediscov- ered method to produce carbonized material at relatively low ∗ Corresponding author at: Freie Universität Berlin, Institut für Biologie, Plant Ecology, Altensteinstr. 6, D-14195 Berlin, Germany. Tel.: +49 030 838 53165; fax: +49 030 838 53886. E-mail address: matthias.rillig@fu-berlin.de (M.C. Rillig). temperatures (180–250 ◦ C) in the presence of water and under pressure (Titirici et al., 2007; Libra et al., 2011). The product is called hydrochar (or HTC-biochar), and likely decomposes more rapidly in soil than biochar (Steinbeiss et al., 2009; Libra et al., 2011). Nevertheless, hydrochar is thought to have broadly similar characteristics as the widely used biochar improving soil biological activity, infiltration, water holding capacity, and cation exchange capacity, which leads to a higher soil fertility and nutrient use effi- ciency (Lehmann, 2007; Libra et al., 2011). In comparison with pyrolysis-derived biochars, HTC materials are more hydrophilic and more hygroscopic due to the higher abundance of polar func- tional groups such as OH, C O and COOH. Furthermore hydrochar material usually has a lower degree of graphitization (Titirici et al., 2008; Baccile et al., 2009). Biochar including hydrochar is thought to act primarily as a soil conditioner and driver of nutrient trans- formation (DeLuca et al., 2009). However, in high dosages there are some reports of negative effects of hydrochar on plant growth (Gajic and Koch, 2012, George et al., 2012). But there is still little information on how the application of carbonized materials affects soil properties, plant productivity and soil biota (Lehmann et al., 0031-4056/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.pedobi.2013.08.003