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Proc Natl Acad Sci U S A. 2007 May 1;104(18):7466-70. Epub 2007 Apr 19.

Changes in nitrogen cycling during the past century in a northern hardwood forest.

Author information

1
Environmental Studies Program, Dartmouth College, 6182 Steele Hall, Hanover, NH 03755, USA. kendra.mclauchlan@dartmouth.edu

Abstract

Nitrogen (N) availability, defined here as the supply of N to terrestrial plants and soil microorganisms relative to their N demands, limits the productivity of many temperate zone forests and in part determines ecosystem carbon (C) content. Despite multidecadal monitoring of N in streams, the long-term record of N availability in forests of the northeastern United States is largely unknown. Therefore, although these forests have been receiving anthropogenic N deposition for the past few decades, it is still uncertain whether terrestrial N availability has changed during this time and, subsequently, whether forest ecosystems have responded to increased N deposition. Here, we used stable N isotopes in tree rings and lake sediments to demonstrate that N availability in a northeastern forest has declined over the past 75 years, likely because of ecosystem recovery from Euro-American land use. Forest N availability has only recently returned to levels forecast from presettlement trajectories, rendering the trajectory of future forest N cycling uncertain. Our results suggest that chronic disturbances caused by humans, especially logging and agriculture, are major drivers of terrestrial N cycling in forest ecosystems today, even a century after cessation.

PMID:
17446271
PMCID:
PMC1863457
DOI:
10.1073/pnas.0701779104
[Indexed for MEDLINE]
Free PMC Article
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