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Harvard Forest Symposium Abstract 2008

  • Title: The Effect of Soil Warming on the Natural Abundance of 15N in Soil, Roots, and Leaves
  • Primary Author: Sarah Butler (Marine Biological Laboratory)
  • Additional Authors: Frank Bowles (Research Designs); Robert Hanifin (Marine Biological Laboratory); Jennifer Johnson (Marine Biological Laboratory); Jerry Melillo (Marine Biological Laboratory); Jacqueline Mohan (University of Georgia); Paul Steudler (Marine Biological Laboratory)
  • Abstract:

    Over the five years of the Barre Woods Soil Warming Experiment at Harvard Forest, net nitrogen mineralization and respiration increased in the heated plots relative to the control. To further understand changes in nitrogen cycling, we analyzed changes in the natural abundances of 15N in the heated and control plots in the soil, roots and tree leaves. Both control and heated plots showed 15N enrichment with increasing soil and root depth, which is consistent with other studies in the Northeast (Nadelhoffer et al. 2004, Pardo et al. 2007, Templer et al. 2007). The 15N values we found in the green leaves on the control plots are in the general range of 15N found in the leaves of other well-studied forested ecosystems in the region (Nadelhoffer et al. 2004, Pardo et al. 2002, Templer et al. 2007). After four years of soil warming, the heated soils were enriched in 15N relative to the control plot. In the heated plot, we also observed a trend towards 15N enrichment in fine roots and their associated microbes and significant 15N enrichment in green leaves of all species analyzed except Acer rubrum. 15N enrichment of the soils in the warmed plots is consistent with our concept of nitrogen isotope fractionation that suggests increased fractionation with increased decomposition (Nadelhoffer and Fry 1988). Enrichment of the roots and leaves suggests an increased uptake of 15N made available by the decomposition of the more recalcitrant, 15N-rich soil carbon pool.

    Works Cited

    Nadelhoffer, K.J. and B. Fry. 1988. Caontrols on natural nitrogen-15 and carbon-13 abundances in forest soil organic matter. Soil Science Society of America Journal 52: 1633-1640.

    Nadelhoffer, 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.

    Pardo, L., H. Hemond, J. Montoya, T. Fahey, and T. Siccama. 2002. Response of the natural abundance of 15N in forest soils and foliage to high nitrate loss following clear-cutting. Canadian Journal of Forest Research 32: 1126-1136.

    Pardo, L.H., H.F. Hemond, J.P. Montoya, and J. Pett-Ridge. 2007. Natural abundance of 15N in soil and litter across a nitrate-output gradient in New Hampshire. Forest Ecology and Management 251: 217-230.

    Templer, P., M. Arthur, G. Lovett, and K. Weathers. 2007. Plant and soil natural abundance δ15N: indicators of relative rates of nitrogen cycling in temperate forest ecosystems. Oecologia 153: 399-40.

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