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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2016-111
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
https://doi.org/10.5194/bg-2016-111
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Submitted as: research article 04 Apr 2016

Submitted as: research article | 04 Apr 2016

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This preprint was under review for the journal BG but the revision was not accepted.

Icelandic grasslands as long-term C sinks under elevated N inputs

Niki I. W. Leblans1,2, Bjarni D. Sigurdsson2, Rien Aerts3, Sara Vicca1, Borgthór Magnússon4, and Ivan A. Janssens1 Niki I. W. Leblans et al.
  • 1Department of Biology, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium
  • 2Faculty of Environmental Sciences, Agricultural University of Iceland, Hvanneyri, 311 Borgarnes, Iceland
  • 3Department of Systems Ecology , Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
  • 4Icelandic Institute of Natural History, Urriðaholtsstræti 6–8, P.O. Box 125, 220 Garðabær, Iceland

Abstract. About 10 % of the anthropogenic CO2 emissions have been absorbed by northern terrestrial ecosystems during the past decades. It has been hypothesized that part of this increasing carbon (C) sink is caused by the alleviation of nitrogen (N) limitation by increasing anthropogenic N inputs. However, little is known about this N-dependent C sink. Here, we studied the effect of chronic seabird-derived N inputs (47–67 kg N ha−1 yr−1) on the net soil organic C (SOC) storage rate of unmanaged Icelandic grasslands on the volcanic Vestmannaeyjar archipelago by using a stock change approach in combination with soil dating. We studied both early developmental soils (50 years) and mature soils (1,600 years), and for the latter we separated between decadal (topsoil) and millennial (total soil profile) responses, where the SOC stocks in the topsoil accorded to 40–50 years of net SOC storage and those in the total soil to 1,600 years of net SOC storage. We found that enhanced N availability – either from accumulation over time, or seabird derived – increased the net SOC storage rate. Under low N inputs, the early developmental soils were weak decadal C sinks (0.018 ton SOC ha−1 yr−1), but this increased quickly under elevated N inputs to 0.29 ton SOC ha−1 yr−1, thereby equaling the decadal SOC storage rate of the unfertilized mature site. Furthermore, at the mature site, chronic N inputs not only stimulated the decadal SOC storage rate, but also the millennial SOC storage was consistently higher at the high N input site. Hence, our study suggests that Icelandic grasslands, if not disturbed, can remain C sinks for many centuries under current climatic conditions and that chronically elevated N inputs can induce a permanent strengthening of this sink.

Niki I. W. Leblans et al.

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Niki I. W. Leblans et al.

Niki I. W. Leblans et al.

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Short summary
Increasing nitrogen (N) deposition has enhanced productivity in many ecosystems and thereby the terrestrial sink for anthropogenic CO2 emissions. However, little is known about how long this N-induced carbon (C) sink can continue. We studied the effect of elevated N inputs on short- (decadal) and long-term (millennial) C storage in Icelandic grasslands and found that chronically elevated N inputs led to a strengthening of this sink for at least 1600 years, in absence of large-scale disturbances.
Increasing nitrogen (N) deposition has enhanced productivity in many ecosystems and thereby the...
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