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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 11 Sep 2019

Submitted as: research article | 11 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Carbon / nitrogen interactions in European forests and semi-natural vegetation. Part I: Fluxes and budgets of carbon, nitrogen and greenhouse gases from ecosystem monitoring and modelling

Chris R. Flechard1, Andreas Ibrom2, Ute M. Skiba3, Wim de Vries4, Marcel van Oijen3, David R. Cameron3, Nancy B. Dise3, Janne F. J. Korhonen5,6, Nina Buchmann7, Arnaud Legout8, David Simpson9,10, Maria J. Sanz11, Marc Aubinet12, Denis Loustau13, Leonardo Montagnani14,15, Johan Neirynck16, Ivan A. Janssens17, Mari Pihlatie5,6, Ralf Kiese18, Jan Siemens19, André-Jean Francez20, Jürgen Augustin21, Andrej Varlagin22, Janusz Olejnik23,24, Radosław Juszczak25, Mika Aurela26, Bogdan H. Chojnicki25, Ulrich Dämmgen27, Vesna Djuricic28, Julia Drewer3, Werner Eugster7, Yannick Fauvel1, David Fowler3, Arnoud Frumau29, André Granier30, Patrick Gross30, Yannick Hamon1, Carole Helfter3, Arjan Hensen29, László Horváth31, Barbara Kitzler32, Bart Kruijt33, Werner L. Kutsch34, Raquel Lobo-do-Vale35, Annalea Lohila36,26, Bernard Longdoz37, Michal V. Marek38, Giorgio Matteucci39, Marta Mitosinkova40, Virginie Moreaux13,41, Albrecht Neftel42, Jean-Marc Ourcival43, Kim Pilegaard2, Gabriel Pita44, Francisco Sanz45, Jan K. Schjoerring46, Maria-Teresa Sebastià47,48, Y. Sim Tang3, Hilde Uggerud49, Marek Urbaniak23, Netty van Dijk3, Timo Vesala36,6, Sonja Vidic28, Caroline Vincke50, Tamás Weidinger51, Sophie Zechmeister-Boltenstern52, Klaus Butterbach-Bahl18, Eiko Nemitz3, and Mark A. Sutton3 Chris R. Flechard et al.
  • 1Institut National de la Recherche Agronomique (INRA), UMR 1069 SAS, 65 rue de Saint-Brieuc, 35042 Rennes, France
  • 2Department of Environmental Engineering, Technical University of Denmark, Bygningstorvet, 2800 Kgs. Lyngby, Denmark
  • 3Centre for Ecology and Hydrology (CEH), Bush Estate, Penicuik, EH26 0QB, UK
  • 4Wageningen University and Research, Environmental Systems Analysis Group, P.O. Box 47, 6700 AA Wageningen, the Netherlands
  • 5Environmental Soil Science, Department of Agricultural Sciences, Faculty of Agriculture and Forestry, P.O. Box 56, 00014 University of Helsinki, Finland
  • 6Institute for Atmospheric and Earth System Research/Forest Sciences, Faculty of Agriculture and Forestry, P.O. Box 27, 00014 University of Helsinki, Finlan
  • 7Department of Environmental Systems Science, Institute of Agricultural Sciences, ETH Zurich, LFW C56, Universitatstr. 2, 8092 Zurich, Switzerland
  • 8INRA, BEF, 54000 Nancy, France
  • 9EMEP MSC-W, Norwegian Meteorological Institute, Oslo, Norway
  • 10Dept. Space, Earth & Environment, Chalmers University of Technology, Gothenburg, Sweden
  • 11Basque Centre for Climate Change (BC3), Scientific Park, Sede Building, s/n Leioa, Bizkaia, Spain
  • 12TERRA Teaching and Research Centre, Gembloux Agro-Bio Tech, University of Liège, Belgium
  • 13Institut National de la Recherche Agronomique (INRA), UMR 1391 ISPA, 33140 Villenave d’Ornon, France
  • 14Forest Services, Autonomous Province of Bolzano, Via Brennero 6, 39100 Bolzano, Italy
  • 15Faculty of Science and Technology, Free University of Bolzano, Piazza Università 5, 39100 Bolzano, Italy
  • 16Research Institute for Nature and Forest (INBO), Gaverstraat 35, 9500 Geraardsbergen, Belgium
  • 17Centre of Excellence PLECO (Plant and Vegetation Ecology), Department of Biology, University of Antwerp, 2610 Wilrijk, Belgium
  • 18Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Kreuzeckbahnstr. 19, 82467 Garmisch-Partenkirchen, Germany
  • 19Institute of Soil Science and Soil Conservation, iFZ Research Centre for Biosystems, Land Use and Nutrition, Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany
  • 20University of Rennes, CNRS, UMR 6553 ECOBIO, Campus de Beaulieu, 263 avenue du Général Leclerc, 35042 45Rennes cedex, France
  • 21Leibniz Centre for Agricultural Landscape Research (ZALF), Eberswalder Straβe 84, 15374, Müncheberg, Germany
  • 22A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, 119071, Leninsky pr.33, Moscow, Russia
  • 23Department of Meteorology, Poznań University of Life Sciences, Piątkowska 94, 60-649 Poznań, Poland
  • 24Department of Matter and Energy Fluxes, Global Change Research Centre, AS CR, v.v.i. Belidla 986/4a, 603 00 Brno, Czech Republic
  • 25Laboratory of Bioclimatology, Department of Ecology and Environmental Protection, Poznan University of Life Sciences, Piatkowska 94, 60-649 Poznan, Poland
  • 26Finnish Meteorological Institute, Climate System Research, PL 503, 00101, Helsinki, Finland
  • 27Weststrasse 5, 38162 Weddel, Germany
  • 28Air Quality Department, Meteorological and Hydrological Service, Gric 3, 10000 Zagreb, Croatia
  • 29TNO, Environmental Modelling, Sensing & Analysis, Petten, the Netherlands
  • 30Institut National de la Recherche Agronomique (INRA), UMR 1434 Silva, Site de Nancy, Rue d'Amance, 54280 Champenoux, France
  • 31Greengrass -Atmospheric Environment Expert Ltd. fellowship, Kornélia utca 14/a, 2030 Érd, Hungary
  • 32Federal Research and Training Centre for Forests, Natural Hazards and Landscape, Seckendorff-Gudent-Weg 8, 1131 Vienna, Austria
  • 33Wageningen University and Research, P.O. Box 47, 6700AA Wageningen, the Netherlands
  • 34Integrated Carbon Observation System (ICOS ERIC) Head Office, Erik Palménin aukio 1, 00560 Helsinki, Finland
  • 35Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal
  • 36Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, P.O. Box 68, 00014 University of Helsinki, Finland
  • 37Gembloux Agro-Bio Tech, Axe Echanges Ecosystèmes Atmosphère, 8, Avenue de la Faculté, 5030 Gembloux, Belgium
  • 38Global Change Research Institute, Academy of Sciences, Bělidla 4a, 603 00 Brno, Czech Republic
  • 39National Research Council of Italy, Institute for Agricultureand Forestry Systems in the Mediterranean (CNR-ISAFOM), Via Patacca, 85 80056 Ercolano (NA), Italy
  • 40Slovak Hydrometeorological Institute, Department of Air Quality, Jeseniova 17, 83315 Bratislava, Slovakia
  • 41Université Grenoble Alpes, CNRS, IGE, 38000 Grenoble, France
  • 42NRE, Oberwohlenstrasse 27, 3033 Wohlen b. Bern, Switzerland
  • 43CEFE, CNRS, Univ Montpellier, Univ Paul Valéry Montpellier 3, EPHE, IRD, Montpellier, France
  • 44Mechanical Engineering Department, Instituto Superior Técnico (Technical University of Lisbon), Ave. Rovisco Pais, IST, 1049-001 Lisboa, Portugal
  • 45Fundacion CEAM, C/ Charles R. Darwin, 46980 Paterna (Valencia), Spain
  • 46Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg C., Denmark
  • 47Laboratory of Functional Ecology and Global Change (ECOFUN), Forest Science and Technology Centre of Catalonia (CTFC), Carretera de Sant Llorenç de Morunys, 25280 Solsona, Spain
  • 48Group GAMES & Department of Horticulture, Botany and Landscaping, School of Agrifood and Forestry Science and Engineering, University of Lleida, Av. Rovira Roure 191, 25198 Lleida, Spain
  • 49Norsk institutt for luftforskning, Postboks 100, 2027 Kjeller, Norway
  • 50Earth and Life Institute (Environmental sciences), Université catholique de Louvain, Louvain-la-Neuve, Belgium
  • 51Department of Meteorology, Eötvös Loránd University, 1117 BudapestPázmány Péter s. 1/A, Hungary
  • 52Institute of Soil Research, Department of Forest and Soil Sciences, University of Natural Resources and Life Sciences Vienna, Peter Jordan Str. 82, 1190 Vienna, Austria

Abstract. The impact of atmospheric reactive nitrogen (Nr) deposition on carbon (C) sequestration in soils and biomass of unfertilised, natural, semi-natural and forest ecosystems has been much debated. Many previous results of this dC / dN response were based on changes in carbon stocks from periodical soil and ecosystem inventories, associated with estimates of Nr deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2019) strive to reduce uncertainties of N effects on C sequestration by linking multi-annual gross and net ecosystem productivity estimates from 40 eddy covariance flux towers across Europe to local measurement-based estimates of dry and wet Nr deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and Nr inputs and losses, these data were also combined with in situ flux measurements of NO, N2O and CH4 fluxes, soil NO3 leaching sampling, as well as results of soil incubation experiments for N and greenhouse gas (GHG) emissions, surveys of available data from online databases and from the literature, together with forest ecosystem (BASFOR) modelling.

Multi-year averages of net ecosystem productivity (NEP) in forests ranged from −70 to 826 g (C) m−2 yr−1 at total wet + dry inorganic Nr deposition rates (Ndep) of 0.3 to 4.3 g (N) m−2 yr−1; and from −4 to 361 g (C) m−2 yr−1 at Ndep rates of 0.1 to 3.1 g (N) m−2 yr−1 in short semi-natural vegetation (moorlands, wetlands and unfertilised extensively managed grasslands). The GHG budgets of the forests were strongly dominated by CO2 exchange, while CH4 and N2O exchange comprised a larger proportion of the GHG balance in short semi-natural vegetation. Nitrogen losses in the form of NO, N2O and especially NO3 were of the order of 10–20 % of Ndep at sites with Ndep < 1 g (N) m−2 yr−1, versus 50–80 % for Ndep > 3 g (N) m−2 yr−1, indicating that perhaps one third of the sites were in a state of early to advanced N saturation. Net ecosystem productivity increased with Nr deposition up to 2–2.5 g (N) m−2 yr−1, with large scatter associated with a wide range in carbon sequestration efficiency (CSE, defined as the NEP / GPP ratio). At elevated Ndep levels (> 2.5 g (N) m−2 yr−1), where inorganic Nr losses were also increasingly large, NEP levelled off and then decreased. The apparent increase in NEP at low to intermediate Ndep levels was partly the result of geographical cross-correlations between Ndep and climate, indicating that the actual mean dC / dN response at individual sites was significantly lower than would be suggested by a simple, straightforward regression of NEP vs. Ndep.

Chris R. Flechard et al.
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Short summary
Experimental evidence from a network of forty monitoring sites in Europe suggests that atmospheric nitrogen deposition to forests and other semi-natural vegetation impacts the carbon sequestration rates in ecosystems, as well as the net greenhouse gas balance including other greenhouse gases such as nitrous oxide and methane. Excess nitrogen deposition in polluted areas also leads to other environmental impacts such as nitrogen leaching to groundwater and other pollutant gaseous emissions.
Experimental evidence from a network of forty monitoring sites in Europe suggests that...