Fungal functioning in a pine forest: evidence from a 15 N ‐labeled global change experiment

Summary We used natural and tracer nitrogen ( N ) isotopes in a P inus taeda free air CO 2 enrichment ( FACE ) experiment to investigate functioning of ectomycorrhizal and saprotrophic fungi in N cycling. Fungal sporocarps were sampled in 2004 (natural abundance and 15 N tracer) and 2010 (tracer) and δ 15 N patterns were compared against litter and soil pools. Ectomycorrhizal fungi with hydrophobic ectomycorrhizas (e.g. C ortinarius and T richoloma ) acquired N from the O ea horizon or deeper. Taxa with hydrophilic ectomycorrhizas acquired N from the O i horizon ( R ussula and L actarius ) or deeper ( L accaria , I nocybe , and A manita ). 15 N enrichment patterns for C ortinarius and A manita in 2010 did not correspond to any measured bulk pool, suggesting that a persistent pool of active organic N supplied these two taxa. Saprotrophic fungi could be separated into those colonizing pine cones ( B aeospora ), wood, litter ( O i), and soil ( R amariopsis ), with δ 15 N of taxa reflecting substrate differences. 15 N enrichment between sources and sporocarps varied across taxa and contributed to δ 15 N patterns. Natural abundance and 15 N tracers proved useful for tracking N from different depths into fungal taxa, generally corresponded to literature estimates of fungal activity within soil profiles, and provided new insights into interpreting natural abundance δ 15 N patterns.