Browsing by Subject "OXIDE FLUXES"

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  • Flechard, Chris R.; Ibrom, Andreas; Skiba, Ute M.; de Vries, Wim; van Oijen, Marcel; Cameron, David R.; Dise, Nancy B.; Korhonen, Janne F. J.; Buchmann, Nina; Legout, Arnaud; Simpson, David; Sanz, Maria J.; Aubinet, Marc; Loustau, Denis; Montagnani, Leonardo; Neirynck, Johan; Janssens, Ivan A.; Pihlatie, Mari; Kiese, Ralf; Siemens, Jan; Francez, Andre-Jean; Augustin, Juergen; Varlagin, Andrej; Olejnik, Janusz; Juszczak, Radoslaw; Aurela, Mika; Berveiller, Daniel; Chojnicki, Bogdan H.; Dammgen, Ulrich; Delpierre, Nicolas; Djuricic, Vesna; Drewer, Julia; Dufrene, Eric; Eugster, Werner; Fauvel, Yannick; Fowler, David; Frumau, Arnoud; Granier, Andre; Gross, Patrick; Hamon, Yannick; Helfter, Carole; Hensen, Arjan; Horvath, Laszlo; Kitzler, Barbara; Kruijt, Bart; Kutsch, Werner L.; Lobo-do-Vale, Raquel; Lohila, Annalea; Longdoz, Bernard; Marek, Michal; Matteucci, Giorgio; Mitosinkova, Marta; Moreaux, Virginie; Neftel, Albrecht; Ourcival, Jean-Marc; Pilegaard, Kim; Pita, Gabriel; Sanz, Francisco; Schjoerring, Jan K.; Sebastia, Maria-Teresa; Tang, Y. Sim; Uggerud, Hilde; Urbaniak, Marek; van Dijk, Netty; Vesala, Timo; Vidic, Sonja; Vincke, Caroline; Weidinger, Tamas; Zechmeister-Boltenstern, Sophie; Butterbach-Bah, Klaus; Nemitz, Eiko; Sutton, Mark A. (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.