, Volume 163, Issue 4, pp 1043–1057 | Cite as

Disentangling drought-induced variation in ecosystem and soil respiration using stable carbon isotopes

  • Stephan Unger
  • Cristina Máguas
  • João S. Pereira
  • Luis M. Aires
  • Teresa S. David
  • Christiane Werner
Ecosystem ecology - Original Paper


Combining C flux measurements with information on their isotopic composition can yield a process-based understanding of ecosystem C dynamics. We studied the variations in both respiratory fluxes and their stable C isotopic compositions (δ13C) for all major components (trees, understory, roots and soil microorganisms) in a Mediterranean oak savannah during a period with increasing drought. We found large drought-induced and diurnal dynamics in isotopic compositions of soil, root and foliage respiration (δ13Cres). Soil respiration was the largest contributor to ecosystem respiration (R eco), exhibiting a depleted isotopic signature and no marked variations with increasing drought, similar to ecosystem respired δ13CO2, providing evidence for a stable C-source and minor influence of recent photosynthate from plants. Short-term and diurnal variations in δ13Cres of foliage and roots (up to 8 and 4‰, respectively) were in agreement with: (1) recent hypotheses on post-photosynthetic fractionation processes, (2) substrate changes with decreasing assimilation rates in combination with increased respiratory demand, and (3) decreased phosphoenolpyruvate carboxylase activity in drying roots, while altered photosynthetic discrimination was not responsible for the observed changes in δ13Cres. We applied a flux-based and an isotopic flux-based mass balance, yielding good agreement at the soil scale, while the isotopic mass balance at the ecosystem scale was not conserved. This was mainly caused by uncertainties in Keeling plot intercepts at the ecosystem scale due to small CO2 gradients and large differences in δ13Cres of the different component fluxes. Overall, stable isotopes provided valuable new insights into the drought-related variations of ecosystem C dynamics, encouraging future studies but also highlighting the need of improved methodology to disentangle short-term dynamics of isotopic composition of R eco.


Keeling plots Respired carbon dioxide Ecosystem respired carbon dioxide stable isotopic composition Drought Mediterranean ecosystem 



Isotopic composition (of respired CO2)


Respiratory flux


Ecosystem respiratory signal


Respiratory signal of ecosystem components








Understory plants


Soil microorganisms


Roots and associated symbionts



This project (ISOFLUX) has been financed by the Deutsche Forschungsgemeinschaft (DFG; WE 2681/2-1). The PIDDAC project (216/2001, Ministério da Agricultura, Portugal, to T. S. David) is acknowledged. The authors wish to thank J. Banza for technical support at the tower, R. Maia for isotope analysis and V. Andrade for flux data treatment. All experiments comply with the current laws of the country in which they were performed.


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Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  • Stephan Unger
    • 1
  • Cristina Máguas
    • 2
  • João S. Pereira
    • 3
  • Luis M. Aires
    • 4
  • Teresa S. David
    • 5
  • Christiane Werner
    • 1
  1. 1.Department of Experimental and Systems EcologyUniversity of BielefeldBielefeldGermany
  2. 2.Centro de Ecologia e Biologia Vegetal, Faculdade de CiênciasUniversidade LisboaLisbonPortugal
  3. 3.Instituto Superior de AgronomiaUniversidade Técnica de LisboaLisbonPortugal
  4. 4.CESAM, Departamento de Engenharia do Ambiente, Escola Superior de Tecnologia e GestãoInstituto Politécnico de LeiriaLeiriaPortugal
  5. 5.Instituto Nacional de Recursos Biológicos, I.P.OeirasPortugal

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