B44D-03:
Evidence for Direct Transfer of Carbon from Surface Litter to Subsoil in Well-Developed Spodosols of Northern Michigan, USA
Thursday, 18 December 2014: 4:30 PM
David Rothstein, Michigan State University, Department of Forestry, East Lansing, MI, United States, Ehsan R Toosi, Michigan State University, Department of Plant, Soil and Microbial Sciences, East Lansing, MI, United States, Randall Schaetzl, Michigan State University, East Lansing, MI, United States and Stuart Grandy, University of New Hampshire, Durham, NH, United States
Abstract:
Traditionally, dissolved organic carbon (DOC) derived from surface litter has been thought to make a major contribution to mineral soil C stores; however, several recent studies have argued that little of the DOC solubilized from surface litter reaches the subsoil directly. We investigated the potential for surface-litter C to contribute to deep-soil C stores in coarse-textured forest soils in northern Michigan, USA. We instrumented six soil profiles, three under coniferous vegetation and three under deciduous vegetation, and measured the quantity and composition of DOC percolating through soil for two years. We used spectroscopic (specific UV absorbance), stable-isotope (natural abundance 13C) and pyrolysis-gas chromatography-mass spectrometry (pyGCMS) analysis of DOC and solid soil samples to assess the degree to which surface-litter C was transported directly through soil vs. the degree to which it exchanged with DOC derived from in situ soil organic C (SOC). All three approaches indicated that surface organic horizons were the source of the majority of DOC entering the B horizon, with little contribution from desorbed SOC en route. Over two years of measurement, we estimate the direct transfer of surface-litter C to the B horizon ranged from 25 g m-2 to 48 g m-2. Interestingly, we observed a strong relationship between the degree of soil development and the composition of DOC entering the B horizon: surface-litter derived C contributed approximately 80% of the DOC entering the B horizon in the most weakly developed profile compared to >95% in the most well-developed profile. This occurred despite the increasing pathlength (i.e. thicker E horizons) associated with increasing spodic development. These findings indicate that the loss of reactive minerals and organic C in the upper profile of well-developed Spodosols promotes the direct transfer of surface C to depth, with little potential for dynamic exchange with in situ SOC.
