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Harvard Forest Symposium Abstract 2010

  • Title: Playing in DIRT: what cross-site experiments can tell us about carbon sequestration
  • Primary Author: Kate Lajtha (Oregon State University)
  • Additional Authors: Richard Bowden (Allegheny College); Susan Crow (University of Hawaii - Manoa); Knute Nadelhoffer (University of Michigan (all campuses)); Alain Plante (The University of Pennsylvania)
  • Abstract:

    Soil organic matter (SOM) contains more reactive organic carbon than any other single terrestrial pool on Earth. Consequently, SOM balance (the difference between accumulation of decaying plant materials and combined losses due to SOM oxidation to CO2 and leaching of dissolved compounds) plays a major role in determining C storage in ecosystems and in regulating atmospheric CO2 concentrations. Despite the critical roles played by SOM within ecosystems, in the global C cycle and in the Earths climate system, controls on SOM balances in ecosystems remain poorly understood. Clearly temperature, soil mineralogy, and land management all play a role in the balance between SOM stabilization and destabilization, but the degree to which plant litter quality and quantity affect soil C sequestration is less well known.

    The central goal of the DIRT (Detrital Inputs and Removal Treatments) experimental network is to assess how rates and sources of plant litter inputs control the long-term stability, accumulation, and chemical nature of soil organic matter in forested ecosystems over decadal time scales. Sites pan climatic and soil gradients, and include the original DIRT experiment established in the Wisconsin Arboretum in 1956, Harvard Forest (1990), Bousson (1991), H.J. Andrews (1997), Skfkt, Hungary (2000), and Michigan (2004). Treatment plots include doubled litter (needle) inputs , doubled wood, no above ground litter (screened) inputs, no root inputs (trenched), and no inputs (screened and trenched).

    A large number of researchers and research projects have used these plots to address mechanisms of SOM stabilization. Density fractionation techniques have been used to determine soil C saturation capacity and storage of both poor and high quality detrital inputs. It appears that in the short term, additional detrital inputs are not stored as long-cycling C but rather as light fraction material. However, there is evidence that over longer time periods (e.g. 50 years) stable C may increase. Studies of respiration have shown priming of older SOM in some ecosystems and not others; microbial community structure changes rapidly with root exclusion, and changes in SOM quality appear to be more rapid in deciduous forests than in coniferous forests. Novel techniques (thermogravitry, SFA analysis) are currently being explored as ways of elucidating mechanisms of soil C sequestration in these forests.

  • Research Category: Soil Carbon and Nitrogen Dynamics