Carbon-nitrogen interactions in European forests and semi-natural vegetation - Part 1: Fluxes and budgets of carbon, nitrogen and greenhouse gases from ecosystem monitoring and modelling
Journal article, 2020
The impact of atmospheric reactive nitrogen (N-r) deposition on carbon (C) sequestration in soils and biomass of unfertilized, 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 N-r deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2020) 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 N-r deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and N-r inputs and losses, these data were also combined with in situ flux measurements of NO, N2O and CH4 fluxes; soil NO3- leaching sampling; and results of soil incubation experiments for N and greenhouse gas (GHG) emissions, as well as surveys of available data from online databases and from the literature, together with forest ecosystem (BAS-FOR) modelling. Multi-year averages of net ecosystem productivity (NEP) in forests ranged from -70 to 826 gCm(-2) yr(-1) at total wet + dry inorganic N-r deposition rates (N-dep) of 0.3 to 4.3 gNm(-2) yr(-1) and from -4 to 361 g Cm-2 yr(-1) at N-dep rates of 0.1 to 3.1 gNm(-2) yr(-1) in short semi-natural vegetation (moorlands, wetlands and unfertilized 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. Uncertainties in elemental budgets were much larger for nitrogen than carbon, especially at sites with elevated N-dep where N-r leaching losses were also very large, and compounded by the lack of reliable data on organic nitrogen and N-2 losses by denitrification. Nitrogen losses in the form of NO, N2O and especially NO3- were on average 27%(range 6 %-54 %) of N-dep at sites with N-dep < 1 gNm(-2) yr(-1) versus 65% (range 35 %-85 %) for N-dep > 3 gNm(-2) yr(-1). Such large levels of N-r loss likely indicate that different stages of N saturation occurred at a number of sites. The joint analysis of the C and N budgets provided further hints that N saturation could be detected in altered patterns of forest growth. Net ecosystem productivity increased with N-r deposition up to 2-2.5 gNm(-2) yr(-1), with large scatter associated with a wide range in carbon sequestration efficiency (CSE, defined as the NEP/GPP ratio). At elevated N-dep levels (> 2.5 gNm(-2) yr(-1)), where inorganic N-r losses were also increasingly large, NEP levelled off and then decreased. The apparent increase in NEP at low to intermediate N-dep levels was partly the result of geographical cross-correlations between N-dep 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. N-dep.
Author
Chris R. Flechard
Inst Natl Rech Agr Alimentat & Environm INRAE
Andreas Ibrom
Technical University of Denmark (DTU)
Ute M. Skiba
UK CEH
Wim de Vries
Wageningen University and Research
Marcel van Oijen
UK CEH
David R. Cameron
UK CEH
Nancy B. Dise
UK CEH
Janne F. J. Korhonen
University of Helsinki
Nina Buchmann
Swiss Federal Institute of Technology in Zürich (ETH)
Arnaud Legout
Inst Natl Rech Agr Alimentat & Environm INRAE
David Simpson
Chalmers, Space, Earth and Environment, Microwave and Optical Remote Sensing
Maria J. Sanz
University of the Basque Country (UPV/EHU)
Marc Aubinet
University of Liège
Denis Loustau
Inst Natl Rech Agr Alimentat & Environm INRAE
Leonardo Montagnani
Free University of Bozen-Bolzano
Autonomous Prov Bolzano
Johan Neirynck
Research Institute for Nature and Forest, Brussels
Ivan A. Janssens
University of Antwerp
Mari Pihlatie
University of Helsinki
Ralf Kiese
Karlsruhe Institute of Technology (KIT)
Jan Siemens
Justus Liebig University Giessen
Andre-Jean Francez
University of Rennes 1
Juergen Augustin
Leibniz Ctr Agr Landscape Res ZALF
Andrej Varlagin
Russian Academy of Sciences
Janusz Olejnik
Poznan University of Life Sciences
AS CR
Radoslaw Juszczak
Poznan University of Life Sciences
Mika Aurela
Finnish Meteorological Institute (FMI)
Daniel Berveiller
University of Paris-Sud
Bogdan H. Chojnicki
Poznan University of Life Sciences
Ulrich Dammgen
Weststr 5
Nicolas Delpierre
University of Paris-Sud
Vesna Djuricic
Meteorol & Hydrol Serv
Julia Drewer
UK CEH
Eric Dufrene
University of Paris-Sud
Werner Eugster
Swiss Federal Institute of Technology in Zürich (ETH)
Yannick Fauvel
Inst Natl Rech Agr Alimentat & Environm INRAE
David Fowler
UK CEH
Arnoud Frumau
Netherlands Organisation for Applied Scientific Research (TNO)
Andre Granier
Inst Natl Rech Agr Alimentat & Environm INRAE
Patrick Gross
Inst Natl Rech Agr Alimentat & Environm INRAE
Yannick Hamon
Inst Natl Rech Agr Alimentat & Environm INRAE
Carole Helfter
UK CEH
Arjan Hensen
Netherlands Organisation for Applied Scientific Research (TNO)
Laszlo Horvath
Greengrass - Atmospheric Environment Expert Ltd. Fellowship
Barbara Kitzler
Fed Res & Training Ctr Forests Nat Hazards & Land
Bart Kruijt
Wageningen University and Research
Werner L. Kutsch
Integrated Carbon Observat Syst ICOS ERIC Head Of
Raquel Lobo-do-Vale
University of Lisbon
Annalea Lohila
Finnish Meteorological Institute (FMI)
University of Helsinki
Bernard Longdoz
Gembloux Agrobio Tech
Marek
Acad Sci
Giorgio Matteucci
National Research Council of Italy (CNR)
Marta Mitosinkova
Slovak Hydrometeorological Institute
Virginie Moreaux
Université Grenoble Alpes
Inst Natl Rech Agr Alimentat & Environm INRAE
Albrecht Neftel
NRE
Jean-Marc Ourcival
University of Montpellier
Kim Pilegaard
Technical University of Denmark (DTU)
Gabriel Pita
Univ Tecn Lisboa
Francisco Sanz
Fdn CEAM
Jan K. Schjoerring
University of Copenhagen
Maria-Teresa Sebastia
Forest Sci & Technol Ctr Catalonia CTFC
Universidad De Lleida
Y. Sim Tang
UK CEH
Hilde Uggerud
Norwegian Institute for Air Research (NILU)
Marek Urbaniak
Poznan University of Life Sciences
Netty van Dijk
UK CEH
Timo Vesala
University of Helsinki
Sonja Vidic
Meteorol & Hydrol Serv
Caroline Vincke
Universite catholique de Louvain
Tamas Weidinger
Eötvös Loránd University (ELTE)
Sophie Zechmeister-Boltenstern
University of Natural Resources and Life Sciences
Klaus Butterbach-Bah
Karlsruhe Institute of Technology (KIT)
Eiko Nemitz
UK CEH
Mark A. Sutton
UK CEH
Biogeosciences
1726-4170 (ISSN) 1726-4189 (eISSN)
Vol. 17 6 1583-1620Subject Categories
Environmental Sciences related to Agriculture and Land-use
Physical Geography
Environmental Sciences
DOI
10.5194/bg-17-1583-2020