Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 12, 2737-2752, 2015
http://www.biogeosciences.net/12/2737/2015/
doi:10.5194/bg-12-2737-2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
11 May 2015
Dynamic C and N stocks – key factors controlling the C gas exchange of maize in heterogenous peatland
M. Pohl1, M. Hoffmann2, U. Hagemann1, M. Giebels1, E. Albiac Borraz1, M. Sommer2,3, and J. Augustin1 1Leibniz Centre for Agriculture Landscape Research (ZALF) e.V., Institute for Landscape Biogeochemistry, Eberswalder Str. 84, 15374 Müncheberg, Germany
2Leibniz Centre for Agriculture Landscape Research (ZALF) e.V., Institute of Soil Landscape Research, Eberswalder Str. 84, 15374 Müncheberg, Germany
3University of Potsdam, Institute of Earth and Environmental Sciences, 14476 Potsdam, Germany
Abstract. The drainage and cultivation of fen peatlands create complex small-scale mosaics of soils with extremely variable soil organic carbon (SOC) stocks and groundwater levels (GWLs). To date, the significance of such sites as sources or sinks for greenhouse gases such as CO2 and CH4 is still unclear, especially if the sites are used for cropland. As individual control factors such as GWL fail to account for this complexity, holistic approaches combining gas fluxes with the underlying processes are required to understand the carbon (C) gas exchange of drained fens. It can be assumed that the stocks of SOC and N located above the variable GWL – defined as dynamic C and N stocks – play a key role in the regulation of the plant- and microbially mediated CO2 fluxes in these soils and, inversely, for CH4. To test this assumption, the present study analysed the C gas exchange (gross primary production – GPP; ecosystem respiration – Reco; net ecosystem exchange – NEE; CH4) of maize using manual chambers for 4 years. The study sites were located near Paulinenaue, Germany, where we selected three soil types representing the full gradient of GWL and SOC stocks (0–1 m) of the landscape: (a) Haplic Arenosol (AR; 8 kg C m−2); (b) Mollic Gleysol (GL; 38 kg C m−2); and (c) Hemic Histosol (HS; 87 kg C m−2). Daily GWL data were used to calculate dynamic SOC (SOCdyn) and N (Ndyn) stocks.

Average annual NEE differed considerably among sites, ranging from 47 ± 30 g C m−2 yr−1 in AR to −305 ± 123 g C m−2 yr−1 in GL and −127 ± 212 g C m−2 yr−1 in HS. While static SOC and N stocks showed no significant effect on C fluxes, SOCdyn and Ndyn and their interaction with GWL strongly influenced the C gas exchange, particularly NEE and the GPP : Reco ratio. Moreover, based on nonlinear regression analysis, 86% of NEE variability was explained by GWL and SOCdyn. The observed high relevance of dynamic SOC and N stocks in the aerobic zone for plant and soil gas exchange likely originates from the effects of GWL-dependent N availability on C formation and transformation processes in the plant–soil system, which promote CO2 input via GPP more than CO2 emission via Reco.

The process-oriented approach of dynamic C and N stocks is a promising, potentially generalisable method for system-oriented investigations of the C gas exchange of groundwater-influenced soils and could be expanded to other nutrients and soil characteristics. However, in order to assess the climate impact of arable sites on drained peatlands, it is always necessary to consider the entire range of groundwater-influenced mineral and organic soils and their respective areal extent within the soil landscape.


Citation: Pohl, M., Hoffmann, M., Hagemann, U., Giebels, M., Albiac Borraz, E., Sommer, M., and Augustin, J.: Dynamic C and N stocks – key factors controlling the C gas exchange of maize in heterogenous peatland, Biogeosciences, 12, 2737-2752, doi:10.5194/bg-12-2737-2015, 2015.
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Short summary
Dynamic SOC and N stocks in the aerobic zone play a key role in the regulation of plant- and microbially mediated CO2 and CH4 fluxes in drained and cultivated fen peatlands. Their interaction with the groundwater level (GWL) strongly influenced soil C gas exchange, indicating effects of GWL-dependent N availability on C formation and transformation processes in the plant--soil system. In contrast, static SOC and N stocks showed no significant effect on C gas fluxes.
Dynamic SOC and N stocks in the aerobic zone play a key role in the regulation of plant- and...
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