Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests

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Anthropogenic nitrogen (N) deposition is increasing rapidly in tropical regions, adding N to ecosystems that often have high background N availability. Tropical forests play an important role in the global carbon (C) cycle, yet the effects of N deposition on C cycling in these ecosystems are poorly understood. We used a field N-fertilization experiment in lower and upper elevation tropical rain forests in Puerto Rico to explore the responses of above- and belowground C pools to N addition. As expected, tree stem growth and litterfall productivity did not respond to N fertilization in either of these Nrich forests, indicating a ... continued below

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Cusack, D.; Silver, W.L.; Torn, M.S. & McDowell, W.H. April 15, 2011.

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Anthropogenic nitrogen (N) deposition is increasing rapidly in tropical regions, adding N to ecosystems that often have high background N availability. Tropical forests play an important role in the global carbon (C) cycle, yet the effects of N deposition on C cycling in these ecosystems are poorly understood. We used a field N-fertilization experiment in lower and upper elevation tropical rain forests in Puerto Rico to explore the responses of above- and belowground C pools to N addition. As expected, tree stem growth and litterfall productivity did not respond to N fertilization in either of these Nrich forests, indicating a lack of N limitation to net primary productivity (NPP). In contrast, soil C concentrations increased significantly with N fertilization in both forests, leading to larger C stocks in fertilized plots. However, different soil C pools responded to N fertilization differently. Labile (low density) soil C fractions and live fine roots declined with fertilization, while mineral-associated soil C increased in both forests. Decreased soil CO2 fluxes in fertilized plots were correlated with smaller labile soil C pools in the lower elevation forest (R2 = 0.65, p\0.05), and with lower live fine root biomass in the upper elevation forest (R2 = 0.90, p\0.05). Our results indicate that soil C storage is sensitive to N deposition in tropical forests, even where plant productivity is not N-limited. The mineral-associated soil C pool has the potential to respond relatively quickly to N additions, and can drive increases in bulk soil C stocks in tropical forests.

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  • Journal Name: Biogeochemistry; Journal Volume: 104; Journal Issue: 1-3; Related Information: Journal Publication Date: 2011

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  • Report No.: LBNL-5143E
  • Grant Number: DE-AC02-05CH11231
  • DOI: 10.1007/s10533-010-9496-4 | External Link
  • Office of Scientific & Technical Information Report Number: 1051650
  • Archival Resource Key: ark:/67531/metadc844274

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  • April 15, 2011

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  • May 19, 2016, 9:45 a.m.

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  • June 16, 2016, 1:28 p.m.

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Cusack, D.; Silver, W.L.; Torn, M.S. & McDowell, W.H. Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests, article, April 15, 2011; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc844274/: accessed September 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.