ORIGINAL PAPER Decomposition of added and native organic carbon from physically separated fractions of diverse soils Sindhu Jagadamma & J. Megan Steinweg & Melanie A. Mayes & Gangsheng Wang & Wilfred M. Post Received: 29 April 2013 /Revised: 8 October 2013 /Accepted: 15 October 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract There have been increasing efforts to understand the dynamics of organic carbon (OC) associated with measur- able fractions of bulk soil. We compared the decomposition of native OC (native C) with that of an added substrate (glucose) on physically separated fractions of a diverse suite of soils. Five soil orders were selected from four contrasting climate zones (Mollisol from temperate, Ultisol and Oxisol from tropics, Andisol from sub-arctic, and Gelisol from arctic re- gion). Soils from the A horizon were fractionated into partic- ulate OC (POC) and mineral-associated OC (MOC) by a size- based method. Fractions were incubated at 20 °C and 50 % water-holding capacity in the dark after the addition of unla- beled D -glucose (0.4 mg C g −1 fraction) and U– 14 C glucose (296 Bq g −1 fraction). Respiration of glucose 14 C indicated 64 to 84 % of added glucose 14 C which was respired from POC and 62 to 70 % from MOC within 150 days of incubation, with more than half of the cumulative respiration occurring within 4 days. Native C respiration varied widely across fractions: 12 to 46 % of native C was respired from POC and 3 to 10 % was respired from MOC fractions. This sug- gested that native C was more stabilized on the MOC than on the POC, but respiration from the added glucose was generally similar for MOC and POC fractions. Our study suggests a fundamental difference between the behavior of freshly added C and native C from MOC and POC fractions of soils. Keywords Native organic carbon . Glucose . Respiration . Particulate organic carbon . Mineral-associated organic carbon Introduction Most soil organic carbon (SOC) compounds are broken down extracellularly by microbial enzymes into simple monomers that can be taken up by microbes. The rate of decomposition can be slowed by inaccessibility of SOC to microorganisms via the physical soil structure and/or through chemical inter- actions with soil minerals, i.e., physical and chemical protec- tion (Lützow et al. 2006; Oades 1988; Sollins et al. 1996). Physical protection involves the spatial segregation of SOC from microorganisms and enzymes by the pore structure and formation of stabilized soil aggregates (Denef and Six 2006; Jastrow 1996; Six et al. 2002; Tisdall and Oades 1982), where the residence time of SOC is strongly linked to aggregate stability (Besnard et al. 1996). Chemical protection involves specific sorption reactions of dissolved organic C (OC) with soil minerals, which reduce bioavailability by inhibiting en- zymatic depolymerization (Jardine et al. 1989; Kaiser and Zech 2000; Kalbitz et al. 2005; Sollins et al. 2009). Positive relationships between OC content and reactive minerals in soils have been observed across a variety of ecosystems (Burke et al. 1989; Ladd et al. 1996; Mayer 1999; Mayes et al. 2012; Oades 1988), which supports the efficacy of minerals to protect SOC from decomposition. S. Jagadamma (*) : M. A. Mayes : G. Wang : W. M. Post Environmental Sciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Rd, PO Box 2008, MS 6036, Oak Ridge, TN 37831, USA e-mail: jagadammas@ornl.gov S. Jagadamma : J. M. Steinweg : M. A. Mayes : G. Wang : W. M. Post Climate Change Science Institute, Oak Ridge National Laboratory, 1 Bethel Valley Rd, PO Box 2008, MS 6036, Oak Ridge, TN 37831, USA J. M. Steinweg Biosciences Division, Oak Ridge National Laboratory, 1 Bethel Valley Rd, PO Box 2008, MS 6036, Oak Ridge, TN 37831, USA Present Address: J. M. Steinweg Department of Biological Sciences, University of Wisconsin- Baraboo/Sauk County, Baraboo, WI 53913, USA Biol Fertil Soils DOI 10.1007/s00374-013-0879-2