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Tree Rings Show Long-term Declines in Forest Nitrogen Availability

For more than a century, human activities have increased atmospheric deposition of nitrogen pollution to forests worldwide. Simultaneously, increased atmospheric carbon dioxide has stimulated plant growth and forest nitrogen uptake. To resolve the net effect of these concurrent global changes on nitrogen availability in forests, scientists evaluated long-term trends in the isotopic composition of nitrogen stored in tree rings at 49 sites across North America. The isotope patterns differed from those expected from plant uptake of atmospherically-deposited nitrogen and excess nitrogen enrichment of soils. Instead, the findings suggest that nitrogen availability in forests has generally declined across much of the United States since at least 1850. This ongoing trend towards lower nitrogen availability in ecosystems is likely to limit forest growth and carbon storage into the future.

McLauchlan, K.K., Gerhart, L.M., Battles, J., Craine, J.M., Elmore, A.J., Higuera, P.E., Mack, M.M., McNeil, B., Nelson, D.M., Pederson, N., Perakis, S.S., 2017, Centennial-scale reductions in nitrogen availability in temperate forests of the United States: Scientific Reports, v. 7, no. 1, p. 7586,[Details]

Contact: Steven Perakis, FRESC, 541-750-0991, Profile

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