Mini-review Microbial responses to a changing environment: implications for the future functioning of terrestrial ecosystems Donald R. ZAK a,b, *, Kurt S. PREGITZER c , Andrew J. BURTON d , Ivan P. EDWARDS a , Harald KELLNER a a School of Natural Resources & Environment, University of Michigan, Ann Arbor, MI 48109, U.S.A. b Department of Ecology and Evolutionary Biology, College of Literature, Science, and Arts, University of Michigan, Ann Arbor, MI 48109, U.S.A. c College of Natural Resources, University of Idaho, Moscow, ID 83844, U.S.A. d Ecosystem Science Center, School of Forest Resources & Environmental Sciences, Michigan Technological University, Houghton, MI 49931, U.S.A. article info Article history: Received 9 November 2010 Revision received 2 March 2011 Accepted 4 March 2011 Available online 11 May 2011 Corresponding editor: Bj € orn Lindahl Keywords: Actinobacteria Ascomycetes Basidiomycetes Biogeochemistry Climate change Extracellular enzymes Fungi Gene transcription Litter decay Nitrogen deposition Soil organic matter storage abstract In this review, we present a conceptual model which links plant communities and sap- rotrophic microbial communities through the reciprocal exchange of growth-limiting resources. We discuss the numerous ways human-induced environmental change has directly and indirectly impacted this relationship, and review microbial responses that have occurred to date. We argue that compositional shifts in saprotrophic microbial communities underlie functional responses to environmental change that have ecosystem-level implications. Drawing on a long-term, large-scale, field experiment, we illustrate how and why chronic atmospheric N deposition can alter saprotrophic communities in the soil of a wide-spread sugar maple (Acer saccharum) ecosystem in northeastern North America, resulting in the slowing of plant litter decay, the rapid accumulation of soil organic matter, and the accelerated production and loss of dissolved organic carbon (DOC). Compositional shifts in soil microbial communities, mediated by ecological interactions among soil saprotrophs, appear to lie at the biogeochemical heart of ecosystem response to environmental change. ª 2011 Elsevier Ltd and The British Mycological Society. All rights reserved. Introduction Soil harbours a phylogenetically diverse community of sap- rotrophic microorganisms whose physiological activities mediate the biogeochemical cycling of carbon (C) and nitrogen (N) at local, regional and global scales. These communities are structured by the physical environment as well as the avail- ability of growth-limiting resources entering soil (i.e., organic * Corresponding author. Tel.: þ1 734 763 4991; fax: þ1 734 936 2195. E-mail address: drzak@umich.edu (D.R. Zak). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/funeco 1754-5048/$ e see front matter ª 2011 Elsevier Ltd and The British Mycological Society. All rights reserved. doi:10.1016/j.funeco.2011.04.001 fungal ecology 4 (2011) 386 e395