Invertebrate grazing affects nitrogen partitioning in the saprotrophic fungus Phanerochaete velutina George M. Tordoff a, b , Paul M. Chamberlain c, d , Thomas W. Crowther a , Helaina I.J. Black e , T. Hefin Jones a , Andrew Stott c , Lynne Boddy a, * a Cardiff School of Biosciences, Cardiff University, Cardiff CF10 3AX, UK b Butterfly Conservation Wales, 10 Calvert Terrace, Swansea SA1 6AR, UK c Life Sciences Mass Spectrometry Facility, Centre for Ecology and Hydrology, CEH Lancaster, Lancaster LA14AP, UK d St Mary’s Thame, Oxfordshire OX9 3AJ, UK e The Macaulay Land Use Research, Craigiebuckler, Aberdeen AB15 8QH, UK article info Article history: Received 20 October 2010 Received in revised form 6 July 2011 Accepted 8 July 2011 Available online xxx Keywords: Collembola Stable isotopes 15 N Mycelium Cord-forming basidiomycetes abstract The heterogeneity of nutrients in forest soils is governed by many biotic and abiotic factors. The significance of nutrient patchiness in determining soil processes remains poorly understood. Some saprotrophic basidiomycete fungi influence nutrient heterogeneity by forming large mycelial networks that enable translocation of nutrients between colonized patches of dead organic matter. The effect of mycophagous soil fauna on these networks and subsequent nutrient redistribution has, however, been little studied. We used a soil microcosm system to investigate the potential effects of a mycophagous collembola, Protaphorura armata, on nutrient transfer within, and nutrient loss from, the mycelium of a saprotrophic basidiomycete fungus, Phanerochaete velutina.A 15 N label, added to central mycelium, was used to track nitrogen movement within the microcosms across 32 days. Although collembola grazing had little impact on d 15 N values, it did alter the partitioning of 15 N between different regions of mycelia. Less 15 N was transferred to new mycelial growth in grazed systems than in ungrazed systems, presumably because collembola reduced fungal growth rate and altered mycelial morphology. Surpris- ingly, collembola grazing did not increase the mineralization of N from mycelium into the bulk soil. Overall, our results suggest that mycophagous soil fauna can alter nutrient flux and partitioning within fungal mycelium; this has the potential to affect the dynamics and spatial heterogeneity of forest floor nutrients. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Soil nitrogen (N) dynamics can influence aboveground net primary productivity (NPP) in woodland ecosystems; increased soil N mineralization, for example, correlates with increased NPP in temperate forests (Pastor et al., 1984; Reich et al., 1997). As forests contain sizeable proportions of the global terrestrial carbon (C) pool (e.g. 55% of carbon stored in vegetation and 45% of that stored in soils (Dixon et al., 1994)), the interaction between forest N and C dynamics is an important factor in climate change predictions. Inter-relations between N and C in soil are spatially-complex due to the patchiness of the soil environment, and relationships between heterogeneity and how soil functions remain little understood (Sulkava and Huhta, 1998; Smithwick et al., 2005). Heterogeneity of soil microbial community composition leads to spatial variation in soil processes such as N mineralization rates (Smithwick et al., 2005). Studies that investigate the effects of environmental heterogeneity on microbially-mediated soil processes rarely consider soil microbes at the level of the indi- vidual organism, due to the microscopic size of most of the species concerned. Some fungi, however, form large and persistent mycelial networks, particularly in forest soils (Smith et al., 1992; Cairney, 2005). One such group is the saprotrophic cord-forming basidiomycetes. These fungi forage for dead organic matter (e.g. wood, leaf litter) on the forest floor, and interconnect discrete patches of these substrata by means of specialized linear organs (cords) that consist of hyphal aggregations (Boddy, 1999). As cord- forming fungi extend they acquire mineral nutrients directly from the soil; they also gain nutrients from the dead organic resources that they decompose and these, together with water, can be rapidly translocated to sites of demand (Wells and Boddy, 1995; Wells et al.,1995, 1997; Donnelly and Boddy, 1998; Tlalka et al., * Corresponding author. Tel.: þ44 (0) 29 2087 4776; fax: þ44 (0) 29 2087 4116. E-mail address: BoddyL@cf.ac.uk (L. Boddy). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio 0038-0717/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2011.07.005 Soil Biology & Biochemistry xxx (2011) 1e9 Please cite this article in press as: Tordoff, G.M., et al., Invertebrate grazing affects nitrogen partitioning in the saprotrophic fungus Phanerochaete velutina, Soil Biology & Biochemistry (2011), doi:10.1016/j.soilbio.2011.07.005