Long-Term Change in the Nitrogen Cycle of Tropical Forests

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Science  04 Nov 2011:
Vol. 334, Issue 6056, pp. 664-666
DOI: 10.1126/science.1211979

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Deposition of reactive nitrogen (N) from human activities has large effects on temperate forests where low natural N availability limits productivity but is not known to affect tropical forests where natural N availability is often much greater. Leaf N and the ratio of N isotopes (δ15N) increased substantially in a moist forest in Panama between ~1968 and 2007, as did tree-ring δ15N in a dry forest in Thailand over the past century. A decade of fertilization of a nearby Panamanian forest with N caused similar increases in leaf N and δ15N. Therefore, our results indicate regional increases in N availability due to anthropogenic N deposition. Atmospheric nitrogen dioxide measurements and increased emissions of anthropogenic reactive N over tropical land areas suggest that these changes are widespread in tropical forests.

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