Nitrogen Addition Increases Carbon Storage in Soils, But Not in Trees, in an Eastern U.S. Deciduous Forest

Gary M. Lovett, Mary A. Arthur, Kathleen C. Weathers, Ross D. Fitzhugh, Pamela H. Templer

Research output: Contribution to journalArticlepeer-review

96 Scopus citations


Forest ecosystems in most industrialized and agricultural regions receive elevated rates of atmospheric nitrogen (N) deposition from air pollution. To evaluate the effects of excess N deposition on carbon (C) and N cycling, we experimentally added N (as NH4NO3) to naturally-occurring, single-species plots of five different tree species that are common in the Northern Hardwood forests of northeastern North America: sugar maple (Acer saccharum Marsh), American beech (Fagus grandifolia Ehrh.), yellow birch (Betula alleghaniensis Britton), eastern hemlock (Tsuga canadensis (L.) Carr), and northern red oak (Quercus rubra L.). The experiment was performed in the Catskill Mountains of southeastern New York State, USA, and used a paired-plot design with six replicate plots per species. After 6 years of treatment, most species showed increases in foliar N concentrations in N-treated plots, but only for maple and birch were those increases statistically significant. No significant effects of the N treatment were observed on woody biomass increment or aboveground net primary production (ANPP) for any species. In the oak plots, the N treatment increased acorn production in mast years. In the soils, the N treatment was associated with a significant decline in potential N mineralization and nitrification rates in the mineral horizon but not in the forest floor, and in the mineral horizon the effect of the N treatment varied among species. The N treatment caused a significant increase in C stock, N stock and C:N ratio in the forest floor, with the largest effect in the hemlock plots. Nitrate leaching increased significantly in treated plots compared to controls. Dissolved organic carbon (DOC) in soil solution was unaffected by the N treatment, but the variation in DOC across plots was correlated with the C stock in the forest floor. These results suggest that the ANPP of these forests is not limited by N availability, but that excess N may cause accumulations of C in the forest floor, particularly in hemlock stands, perhaps through inhibition of decomposition rates or by altering phenolic chemistry of the litter. The magnitude, and sometimes the direction of the N treatment responses varied among species, suggesting that predictions of forest responses to elevated N deposition should take into account spatial and temporal variation in tree species composition.

Original languageEnglish
Pages (from-to)980-1001
Number of pages22
Issue number6
StatePublished - Sep 2013

Bibliographical note

Funding Information:
We thank the US Department of Agriculture National Research Initiative, the National Science Foundation (DEB9981503 and DEB0444895), the USDA Forest Service Northeastern States Research Cooperative, and the A.W. Mellon Foundation for support for this work. We are grateful to the many students and research assistants who have helped with this work over the years, especially Chuck Schirmer, Jake Griffin, Brent Mellen, Jessica Hancock, Greg Abernathy, Miriam Osredkar, Margaret Ward, and Milinda Hamilton. We thank Dr. Jack Schultz for analysis of phenolic concentrations in litter.


  • Catskill mountains
  • carbon
  • fertilization
  • forest
  • nitrogen
  • nitrogen deposition

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Environmental Chemistry
  • Ecology


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