Effects of nutrient-rich substrate and ectomycorrhizal symbiosis on spruce seedling biomass in abandoned nests of the wood ant (Formica polyctena): a laboratory experiment Veronika Jílková a, ⁎, Jan Frouz a,b , Ondřej Mudrák c , Martin Vohník d,e a Institute for Environmental Studies, Faculty of Science, Charles University in Prague, Benátská 2, CZ-12801 Prague, Czech Republic b Institute of Soil Biology, The Czech Academy of Sciences, Na Sádkách 7, CZ-37005 České Budějovice, Czech Republic c Department of Functional Ecology, Institute of Botany, The Czech Academy of Sciences, Dukelská 135, CZ-37982 Třeboň, Czech Republic d Department of Mycorrhizal Symbioses, Institute of Botany, The Czech Academy of Sciences, Lesní 322, CZ-25243 Průhonice, Czech Republic e Department of Plant Experimental Biology, Faculty of Science, Charles University in Prague, Viničná 5, CZ-12844 Prague, Czech Republic abstract article info Article history: Received 11 March 2015 Received in revised form 8 May 2015 Accepted 12 May 2015 Available online xxxx Keywords: EcM Nutrient uptake Ergosterol Moisture Phosphorus Potassium Coniferous trees can take up mineral nutrients either non-symbiotically from nutrient-rich hotspots in the forest floor or via symbiosis with ectomycorrhizal (EcM) fungi; EcM symbiosis also enables the trees to obtain nutrients from organic substances. Excellent examples of nutrient-rich forest-floor hotspots are abandoned wood ant nests, which accumulate significant amounts of inorganic substances that are readily accessible to roots as well as organic substances that are not accessible to non-mycorrhizal roots. We examined the effects of substrates from abandoned nests of the wood ant Formica polyctena and EcM symbiosis on the growth of Norway spruce (Picea abies) seedlings. The tested substrates originated from the centers and rims of wet and dry ant nests, and from the surrounding forest floor. Aseptic spruce seedlings were grown in these substrates in a growth chamber, and after 7 months, seedling biomass, the chemical and microbiological properties of the substrates, and EcM colonization and diversity were determined. Spruce seedlings grew better and had a more diverse spectra of EcM fungi in the ant nest substrates than in the forest floor substrate. Substrate nutrient content, especially phosphorus and basic cations, positively correlated with spruce biomass, EcM diversity, and fungal biomass. Contrary to conventional wisdom, high nutrient contents in ant nests apparently enhanced EcM abundance and diversity. Although abandoned wood ant nests in temperate and boreal forests are not abundant and thus are unlikely to have ecosystem level effects, they may cause significant local variations in tree growth and in the occurrence of root-symbiotic fungi. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Temperate and boreal coniferous forests usually occur on acidic soils (Brady and Weil, 2002). As needle litter decomposes, fulvic acids are released and nutrients that bind to the acids are leached from the topsoil. The low pH of forest soils is unfavorable for nutrient exploitation by plant roots because the nutrients, and especially phosphorus (P), bind to aluminum or iron and form insoluble complexes. Because of these and similar processes, soils of most climax coniferous forests become nutrient-limited. The most important nutrients that limit the productivity of coniferous trees are nitrogen (N) (McGroddy et al., 2004) and P (Batjes, 1997). A key factor in nutrient uptake by trees is the absorption ability of the roots (Bowen, 1984). To increase absorption ability, most temperate and boreal tree species form symbioses with ectomycorrhizal (EcM) fungi (Smith and Read, 2008). In exchange for plant photosynthetically bound carbon (C), EcM fungi provide their hosts with otherwise inac- cessible organically bound nutrients and also with increased resistance against pathogens and drought. EcM fungi produce an extraradical mycelium, which explores the surrounding soil at greater distances than non-mycorrhizal roots and facilitates nutrient exploitation (Plassard and Dell, 2010). Another key factor in nutrient uptake by trees is the availability of nutrients in the soil (Bowen, 1984). Nutrient availability can be high at nutrient-rich hotspots in the forest floor, such as wood ant nests. Wood ants (Formica s. str., Formicidae, Hymenoptera) inhabiting temperate and boreal forests build large (mean volume per nest = 1m 3 ) and long-lasting nests from plant materials, and forage for honeydew and prey to feed the colony (Frouz and Jílková, 2008). Plant materials and food residues decompose in nests because of favorable microclimatic conditions and enhanced microbial activity, so that mineral nutrients are released (Domisch et al., 2008; Jílková and Frouz, 2014). Moreover, pH is higher in ant nests than in the forest Geoderma 259–260 (2015) 56–61 ⁎ Corresponding author. E-mail address: jilkova.veronika@gmail.com (V. Jílková). http://dx.doi.org/10.1016/j.geoderma.2015.05.007 0016-7061/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma