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
Flechard, C. R.; Ibrom, A.; Skiba, U. M.; De Vries, W.; Van Oijen, M.; Cameron, D. R.; DIse, N. B.; Korhonen, J. F. J.; Buchmann, N.; Legout, A.; Simpson, D.; Sanz, M. J.; Aubinet, M.; Loustau, D.; Montagnani, L.; Neirynck, J.; Janssens, I. A.; Pihlatie, M.; Kiese, R. 1,2; ... mehrSiemens, J.; Francez, A.-J.; Augustin, J.; Varlagin, A.; Olejnik, J.; Juszczak, R.; Aurela, M.; Berveiller, D.; Chojnicki, B. H.; Dämmgen, U.; Delpierre, N.; Djuricic, V.; Drewer, J.; Dufrêne, E.; Eugster, W.; Fauvel, Y.; Fowler, D.; Frumau, A.; Granier, A.; Gross, P.; Hamon, Y.; Helfter, C.; Hensen, A.; Horvath, L.; Kitzler, B.; Kruijt, B.; Kutsch, W. L.; Lobo-Do-Vale, R.; Lohila, A.; Longdoz, B.; Marek, M. V.; Matteucci, G.; Mitosinkova, M.; Moreaux, V.; Neftel, A.; Ourcival, J.-M.; Pilegaard, K.; Pita, G.; Sanz, F.; Schjoerring, J. K.; Sebastià, M.-T.; Sim Tang, Y.; Uggerud, H.; Urbaniak, M.; Van DIjk, N.; Vesala, T.; Vidic, S.; Vincke, C.; Weidinger, T.; Zechmeister-Boltenstern, S.; Butterbach-Bahl, K. 1; Nemitz, E.; Sutton, M. A.
1 Institut für Meteorologie und Klimaforschung (IMK), Karlsruher Institut für Technologie (KIT)
2 Institut für Meteorologie und Klimaforschung – Atmosphärische Umweltforschung (IMK-IFU), Karlsruher Institut für Technologie (KIT)
Abstract:
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, N$_{2}$O and CH$_{4}$ fluxes; soil NO$_{3}$̅ 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 (BASFOR) modelling. ... mehrMulti-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 CO$_{2}$ exchange, while CH$_{4}$ and N$_{2}$O 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, N$_{2}$O and especially NO$_{3}$̅ 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$_{dep}$.
Zugehörige Institution(en) am KIT |
Institut für Meteorologie und Klimaforschung – Atmosphärische Umweltforschung (IMK-IFU) Universität Karlsruhe (TH) – Interfakultative Einrichtungen (Interfakultative Einrichtungen) KIT-Zentrum Klima und Umwelt (ZKU) |
Publikationstyp |
Zeitschriftenaufsatz |
Publikationsjahr |
2020 |
Sprache |
Englisch |
Identifikator |
ISSN: 1726-4170, 1726-4189
KITopen-ID: 1000118975 |
HGF-Programm |
12.02.01 (POF III, LK 01) Effects of land use and climate change |
Erschienen in |
Biogeosciences |
Verlag |
Copernicus Publications |
Band |
17 |
Heft |
6 |
Seiten |
1583-1620 |
Nachgewiesen in |
Dimensions Scopus Web of Science
|