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Harvard Forest Symposium Abstract 2019

  • Title: The Detrital Input and Removal Treatment (DIRT) Project: Exploring Soil C Storage and Chemistry
  • Primary Author: Richard Bowden (Allegheny College)
  • Additional Authors: Kate Lajtha (Oregon State University); Knute Nadelhoffer (University of Michigan (all campuses))
  • Abstract:

    Richard D. Bowden, Myrna Simpson, Knute Nadelhoffer, Alain F. Plante, Susan Crow, Lauren Deem, Andre Simpson, István Fekete, Zsolt Kotroczó, Jun-Jian Wang, Oliva Pisani, Lisa H. Lin, Olivia O.Y. Lun, Kate Lajtha

    Soils contain large reservoirs of the global carbon store, yet land use change and unsustainable land use practices have reduced this C pool. Despite these human influences, factors that control both the content as well as the chemistry of soil C are still poorly quantified. The Detrital Input and Removal Treatment (DIRT) Project was established to evaluate rates and sources of plant litter inputs on soil organic matter (SOM) content and chemistry across a range of ecosystem and soil types. Litter is added or excluded from permanent plots (Fig. 1), and total SOM and soil organic chemistry have been measured across a range of both US and international sites.

    Across the DIRT network, SOM pools responded only slightly, or not at all, to chronic doubling of aboveground litter inputs (Fig. 2). The slow or even negative response of SOM to litter additions is driven by increased decomposition (Fig. 3), priming (increased microbial utilization of old SOM following inputs of new organic matter inputs), and increased leaching of dissolved organic C. Evidence of priming includes accelerated soil respiration in litter addition plots, decreased dissolved organic carbon output from increased microbial activity, and biochemical markers in soil indicating enhanced SOM degradation (Fig 4). SOM pools decreased in response to exclusion of aboveground litter, which had a greater effect on soil C than did excluding roots, indicating that in these ecosystems, root-derived C is not more critical than aboveground litter C to soil C sequestration. The chemistry of SOM is dynamic, altered microbially through priming by increased inputs, as well as by increased degradation through reduced inputs. Partitioning of belowground contributions to total soil respiration were predictable based on site-level soil C and N as estimates of site fertility. Contributions to soil respiration from root respiration were negatively related to soil fertility and contributions from decomposing aboveground litter in soil were positively related to site fertility.

    The DIRT project, begun historically at the U. Wisconsin Arboretum and expanded initially into its modern set of treatments at the Harvard Forest, has provided valuable insights into forest soil C processes. Our work suggests that efforts to enhance forest productivity have a limited potential to accelerate soil C storage in mature forests. Conversely, reductions in organic matter inputs, as might be driven by environmental changes that reduce forest productivity, will reduce soil C content.

  • Research Category: Soil Carbon and Nitrogen Dynamics

  • Figures:
  • HF 2019 Abstract - Bowden - Figure 1.docx
    HF 2019 Abstract - Bowden - Figure 2.docx
    HF 2019 Abstract - Bowden - Figure 3.docx
    HF 2019 Abstract - Bowden - Figure 4.docx