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Anthropogenic nitrogen deposition in boreal forests has a minor impact on the global carbon cycle
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
2014 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 20, no 1, 276-286 p.Article in journal (Refereed) Published
Abstract [en]

It is proposed that increases in anthropogenic reactive nitrogen (N-r) deposition may cause temperate and boreal forests to sequester a globally significant quantity of carbon (C); however, long-term data from boreal forests describing how C sequestration responds to realistic levels of chronic N-r deposition are scarce. Using a long-term (14-year) stand-scale (0.1ha) N addition experiment (three levels: 0, 12.5, and 50kgNha(-1)yr(-1)) in the boreal zone of northern Sweden, we evaluated how chronic N additions altered N uptake and biomass of understory communities, and whether changes in understory communities explained N uptake and C sequestration by trees. We hypothesized that understory communities (i.e. mosses and shrubs) serve as important sinks for low-level N additions, with the strength of these sinks weakening as chronic N addition rates increase, due to shifts in species composition. We further hypothesized that trees would exhibit nonlinear increases in N acquisition, and subsequent C sequestration as N addition rates increased, due to a weakening understory N sink. Our data showed that understory biomass was reduced by 50% in response to the high N addition treatment, mainly due to reduced moss biomass. A N-15 labeling experiment showed that feather mosses acquired the largest fraction of applied label, with this fraction decreasing as the chronic N addition level increased. Contrary to our hypothesis, the proportion of label taken up by trees was equal (ca. 8%) across all three N addition treatments. The relationship between N addition and C sequestration in all vegetation pools combined was linear, and had a slope of 16kgCkg(-1)N. While canopy retention of N-r deposition may cause C sequestration rates to be slightly different than this estimate, our data suggest that a minor quantity of annual anthropogenic CO2 emissions are sequestered into boreal forests as a result of N-r deposition.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2014. Vol. 20, no 1, 276-286 p.
Keyword [en]
N-15 labeling, carbon sequestration, carbon sink, dwarf shrubs, feather mosses, Nitrogen deposition, productivity, soil nitrogen uptake, understory vegetation
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:umu:diva-84761DOI: 10.1111/gcb.12422ISI: 000327998600025OAI: diva2:695164
Available from: 2014-02-10 Created: 2014-01-20 Last updated: 2014-02-10Bibliographically approved

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Gundale, Michael J.Bach, Lisbet H.
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