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

Niki I.W. Leblans*, Bjarni D. Sigurdsson, Rien Aerts, Sara Vicca, Borgthór Magnússon, Ivan A. Janssens

*Corresponding author for this work

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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 year−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 (young) soils that had been receiving increased N inputs over a decadal timescale since an eruption in 1963, and well-developed soils, that had been receiving N inputs over a millennial timescale. For the latter, however, the effects on both decadal (topsoil; 40 years) and millennial (total soil profile; 1600 years) SOC storage could be studied, as the age of topsoil and the total soil profile could be determined from volcanic ash layers deposited in 1973 and 395 AD. We found that enhanced N availability—either from accumulation over time, or seabird derived—increased the net SOC storage rate. Under low N inputs, early developmental soils were weak decadal C sinks (0.018 ton SOC ha−1 year−1), but this increased quickly under ca. 30 years of elevated N inputs to 0.29 ton SOC ha−1 year−1, thereby equalling the decadal SOC storage rate of the unfertilized well-developed soils. Furthermore, for the well-developed soils, chronically elevated N inputs not only stimulated the decadal SOC storage rate in the topsoil, but also the total millennial SOC storage was consistently higher. 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.

Original languageEnglish
Pages (from-to)279-299
Number of pages21
Issue number3
Early online date27 Jul 2017
Publication statusPublished - Aug 2017


This research was supported by the Research Foundation—Flanders (FWO aspirant grant to NL; FWO postdoctoral fellowship to SV), the European Research Council Synergy grant 610028 (IMBALANCE-P), and the Research Council of the University of Antwerp. We acknowledge support from FSC-Sink, CAR-ES and the ClimMani COST Action E1308. The Surtsey Research Society, Institute of Natural History, Mogilsá—Icelandic Forest Research, Reykir and Keldnaholt—Agricultural University of Iceland and the Icelandic Coastguard provided logistical support for the present study. We thank Sturla Fridriksson, Sigurdur Magnússon and Erling Ólafsson for generously providing access to their data. We are grateful to Anette Th. Meier for designing the map. We thank Annemie Vinck, Paul Leblans, Pieter Roefs, Rafaële Thuys, Elín Guðmundsdóttir, Elías Óskarsson, Sigurður Sturla Bjarnasson, Hekla Hrund Bjarnadóttir, Alexander Meire, Damiano Cillio, Linde Leblans and Dries De Pauw for their helping hands in the field. Further, we thank Brita Berglund, Baldur Vigfusson, Nadine Calluy, Marijke Van den Bruel and Els Oosterbos for their assistance with the lab analyses.

FundersFunder number
Research Council of the University of Antwerp
Research Foundation—Flanders
Seventh Framework Programme610028
European Research Council
European Cooperation in Science and TechnologyE1308
Fonds Wetenschappelijk Onderzoek


    • Long-term carbon storage
    • N inputs
    • Soil development
    • Surtsey
    • Terrestrial C sink


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