Articles | Volume 6, issue 6
Biogeosciences, 6, 1027–1041, 2009

Special issue: Carbon cycling in Sub-Saharan Africa

Biogeosciences, 6, 1027–1041, 2009

  18 Jun 2009

18 Jun 2009

Precipitation as driver of carbon fluxes in 11 African ecosystems

L. Merbold1, J. Ardö2, A. Arneth2, R. J. Scholes3, Y. Nouvellon4,5, A. de Grandcourt4,5, S. Archibald3, J. M. Bonnefond6, N. Boulain7, N. Brueggemann8, C. Bruemmer16, B. Cappelaere7, E. Ceschia9, H. A. M. El-Khidir10, B. A. El-Tahir10, U. Falk11, J. Lloyd14, L. Kergoat9, V. Le Dantec9, E. Mougin9, M. Muchinda12, M. M. Mukelabai12, D. Ramier7, O. Roupsard4,15, F. Timouk9, E. M. Veenendaal13, and W. L. Kutsch1 L. Merbold et al.
  • 1Max-Planck Institute for Biogeochemistry, P.O. Box 100164, 07701 Jena, Germany
  • 2Department of Physical Geography and Ecosystems Analysis, Lund University Sölvegatan 12, 22362, Lund, Sweden
  • 3Natural Resources and Environment, CSIR, P.O. Box 395, Pretoria, South Africa
  • 4CIRAD, Persyst, UPR80, TA B-80/D, 34398 Montpellier Cedex 5, France
  • 5UR2PI, BP 1291, Pointe-Noire, Republic of Congo
  • 6INRA-EPHYSE, BP 81, 33883 Villenave d'Ornon Cedex, France
  • 7UMR Hydrosciences, IRD, BP 64501, 34394 Monpellier Cedex 5, France
  • 8Atmospheric Environmental Research Division, Institute of Meteorology and Climate Research, Forschungszentrum Karlsruhe, Garmisch-Partenkirchen, Germany
  • 9CESBIO, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France
  • 10Agricultural Research Cooperation, El Obeid Research Station, P.O. Box 429, 51111, El Obeid, Sudan
  • 11Department of Ecology and Resource Management, Center for Development Research, University of Bonn, Bonn, Germany
  • 12Zambia Meteorological Department, Haile Sellasie Avenue, City Airport, P. O. Box 30200, 10101 Lusaka, Zambia
  • 13Nature Conservation and Plant Ecology Group, Wageningen University, Droevendaalse Steeg 3a, 6708 PD Wageningen, The Netherlands
  • 14Earth and Biosphere Institute, School of Geography, University of Leeds, LS29JT, UK
  • 15CATIE, 7170 Turrialba, Costa Rica
  • 16Biometeorology and Soil Physics Group, Faculty of Land and Food Systems, University of British Columbia, V6T 1ZA, Vancouver, Canada

Abstract. This study reports carbon and water fluxes between the land surface and atmosphere in eleven different ecosystems types in Sub-Saharan Africa, as measured using eddy covariance (EC) technology in the first two years of the CarboAfrica network operation. The ecosystems for which data were available ranged in mean annual rainfall from 320 mm (Sudan) to 1150 mm (Republic of Congo) and include a spectrum of vegetation types (or land cover) (open savannas, woodlands, croplands and grasslands). Given the shortness of the record, the EC data were analysed across the network rather than longitudinally at sites, in order to understand the driving factors for ecosystem respiration and carbon assimilation, and to reveal the different water use strategies in these highly seasonal environments.

Values for maximum net carbon assimilation rates (photosynthesis) ranged from −12.5 μmol CO2 m−2 s−1 in a dry, open Millet cropland (C4-plants) up to −48 μmol CO2 m−2 s−1 for a tropical moist grassland. Maximum carbon assimilation rates were highly correlated with mean annual rainfall (r2=0.74). Maximum photosynthetic uptake rates (Fpmax) were positively related to satellite-derived fAPAR. Ecosystem respiration was dependent on temperature at all sites, and was additionally dependent on soil water content at sites receiving less than 1000 mm of rain per year. All included ecosystems dominated by C3-plants, showed a strong decrease in 30-min assimilation rates with increasing water vapour pressure deficit above 2.0 kPa.

Final-revised paper