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Harvard Forest Symposium Abstract 2009

  • Title: Nitrogen Saturation—A 20-year Synthesis
  • Primary Author: Serita Frey (University of New Hampshire - Main Campus)
  • Additional Authors: Richard Bowden (Allegheny College); Bryan Dail (University of Maine); Michelle Day (University of New Hampshire - Main Campus); Adrien Finzi (Boston University); Christine Goodale (Cornell University); Kate Lajtha (Oregon State University); Jim LeMoine (University of Michigan (all campuses)); Rich MacLean (University of New Hampshire - Main Campus); William McDowell (University of New Hampshire - Main Campus); Knute Nadelhoffer (University of Michigan (all campuses)); Scott Ollinger (University of New Hampshire - Main Campus); Pamela Templer (Boston University); Susan Trumbore (University of California - Irvine); Marissa Weiss (Cornell University)
  • Abstract:

    This past year marked the 20th anniversary of the Chronic Nitrogen Addition Experiment at Harvard Forest. In recognition of this anniversary, an intensive sampling campaign was organized with a focus on evaluating how the long-term N additions have impacted ecosystem C storage and N dynamics. Located in an old red pine plantation and a mixed hardwood forest the treated plots have received 50 and 150 kg N•ha-1•yr-1, as NH4NO3, in six equal monthly applications during the growing season each year since the start of the experiment. Additionally, the control and low N treatments were given a single pulse label of 15NO3 and 15NH4 in 1991 and 1992. Regular measurements have been made over the past 20 years to assess woody biomass production and mortality, foliar chemistry, litter fall, and soil N dynamics. Less frequent measurements of soil C pools, soil respiration, fine root dynamics, and microbial biomass and community structure have been made. Results from the first 15 years of the experiment were synthesized in a special issue of Forest Ecology and Management1.

    This experiment was initiated in 1988 to better understand the process of forest N saturation due to anthropogenic N deposition. The longevity of the experiment has enhanced its value because of the current uncertainty regarding the degree to which N deposition has and will continue to alter C storage in temperate forests. Thus a primary objective of our 2008 sampling effort was to assess the amount of C stored in wood, foliage, litter, roots, and soil (to a depth of ~50 cm). We also wanted to examine the fate of N by comparing patterns of 15N recovery to those observed previously2,3. An additional objective was to further examine how chronic N additions impact microbial biomass, activity and community structure. Results to date will be presented at the symposium.

    1Aber, J.D. (ed). 2004. The Harvard Forest (USA) Nitrogen Saturation Experiment: Results from the First 15 Years. Forest Ecology and Management 196, 1-186.

    2Nadelhoffer, K.J., M.R. Downs, and M.R. Fry. 1999. Sinks for N-15 enriched additions to an oak forest and a red pine plantation. Ecological Applications 9, 72-86.

    3Nadelhoffer, K.J., B.P. Colman, W.S. Currie, A. Magill, and J.D. Aber. 2004. Decadal-scale fates of 15N tracers added to oak and pine stands under ambient and elevated N inputs at the Harvard Forest (USA). Forest Ecology and Management 196, 89-107

  • Research Category: Large Experiments and Permanent Plot Studies, Soil Carbon and Nitrogen Dynamics