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    Author(s): Daniela F. Cusack; Whendee L. Silver; Margaret S. Torn; William H. McDowell
    Date: 2011
    Source: Biogeochemistry
    Publication Series: Scientific Journal (JRNL)
    Station: International Institute of Tropical Forestry
    PDF: View PDF  (514.0 KB)

    Description

    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.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    Cusack, Daniela F.; Silver, Whendee L.; Torn, Margaret S.; McDowell, William H. 2011.Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests. Biogeochemistry. 104(1-3): 203-225. https://doi.org/10.1007/s10533-010-9496-4.

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    Keywords

    Aboveground biomass, Dissolved organic carbon, Nutrient limitation, Roots, Soil density, fractions, Soil respiration.

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