Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 12, issue 16
Biogeosciences, 12, 5041–5059, 2015
https://doi.org/10.5194/bg-12-5041-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 12, 5041–5059, 2015
https://doi.org/10.5194/bg-12-5041-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 26 Aug 2015

Research article | 26 Aug 2015

The influence of C3 and C4 vegetation on soil organic matter dynamics in contrasting semi-natural tropical ecosystems

G. Saiz2,1, M. Bird3, C. Wurster3, C. A. Quesada4, P. Ascough5, T. Domingues6, F. Schrodt7, M. Schwarz7, T. R. Feldpausch8, E. Veenendaal9, G. Djagbletey10, G. Jacobsen11, F. Hien12, H. Compaore12, A. Diallo13, and J. Lloyd14,15 G. Saiz et al.
  • 1Institute Meteorology and Climate Research, Karlsruhe Institute of Technology, Garmisch-Partenkirchen 82467, Germany
  • 2School of Geography & Geosciences, University of St Andrews, St Andrews, KY16 9AL, Scotland, UK
  • 3College of Science, Technology and Engineering and Centre for Tropical Environmental and Sustainability Science, James Cook University, Cairns, QLD 4870, Australia
  • 4Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil
  • 5SUERC, Scottish Enterprise Technology Park, Rankine Avenue, East Kilbride G75 0QF, UK
  • 6School of GeoSciences, University of Edinburgh, Drummond Street, Edinburgh, EH8 9XP, Scotland, UK
  • 7Earth and Biosphere Institute, School of Geography, University of Leeds, LS2 9JT, Leeds, UK
  • 8College of Life and Environmental Sciences, University of Exeter, UK
  • 9Nature Conservation and Plant Ecology Group, Wageningen University, the Netherlands
  • 10Forestry Research Institute of Ghana, Kumasi, Ghana
  • 11ANSTO Institute for Environmental Research, PMB 1, Menai NSW 2234, Australia
  • 12Institut de l'Environnement et de Recherches Agricoles, Ouagadougou, Burkina Faso
  • 13Centre National des Semences Forestières, Ouagadougou, Burkina Faso
  • 14Department of Life Sciences, Imperial College London, UK
  • 15School of Marine and Tropical Biology, James Cook University, Cairns, QLD 4870, Australia

Abstract. Variations in the carbon isotopic composition of soil organic matter (SOM) in bulk and fractionated samples were used to assess the influence of C3 and C4 vegetation on SOM dynamics in semi-natural tropical ecosystems sampled along a precipitation gradient in West Africa. Differential patterns in SOM dynamics in C3/C4 mixed ecosystems occurred at various spatial scales. Relative changes in C / N ratios between two contrasting SOM fractions were used to evaluate potential site-scale differences in SOM dynamics between C3- and C4-dominated locations. These differences were strongly controlled by soil texture across the precipitation gradient, with a function driven by bulk δ13C and sand content explaining 0.63 of the observed variability. The variation of δ13C with soil depth indicated a greater accumulation of C3-derived carbon with increasing precipitation, with this trend also being strongly dependant on soil characteristics. The influence of vegetation thickening on SOM dynamics was also assessed in two adjacent, but structurally contrasting, transitional ecosystems occurring on comparable soils to minimise the confounding effects posed by climatic and edaphic factors. Radiocarbon analyses of sand-size aggregates yielded relatively short mean residence times (τ) even in deep soil layers, while the most stable SOM fraction associated with silt and clay exhibited shorter τ in the savanna woodland than in the neighbouring forest stand. These results, together with the vertical variation observed in δ13C values, strongly suggest that both ecosystems are undergoing a rapid transition towards denser closed canopy formations. However, vegetation thickening varied in intensity at each site and exerted contrasting effects on SOM dynamics. This study shows that the interdependence between biotic and abiotic factors ultimately determine whether SOM dynamics of C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM.

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We demonstrate and explain differential patterns in SOM dynamics in C3/C4 mixed ecosystems at various spatial scales across contrasting climate and soils. This study shows that the interdependence between biotic and abiotic factors ultimately determines whether SOM dynamics of C3- and C4-derived vegetation are at variance in ecosystems where both vegetation types coexist. The results also highlight the far-reaching implications that vegetation thickening may have for the stability of deep SOM.
We demonstrate and explain differential patterns in SOM dynamics in C3/C4 mixed ecosystems at...
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