Importance of short-term dynamics in carbon isotope ratios of ecosystem respiration (δ13CR) in a Mediterranean oak woodland and linkage to environmental factors

Authors

  • Christiane Werner,

    1. Exp. and Systems Ecology, University of Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany;
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  • Stephan Unger,

    1. Exp. and Systems Ecology, University of Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany;
    2. Centro de Ecologia e Biologia Vegetal, Faculdade de Ciências, Universidade Lisboa, Campo Grande, P-1749-016 Lisbon, Portugal;
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  • João S. Pereira,

    1. Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal;
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  • Rodrigo Maia,

    1. ICAT-Instituto de Ciência Aplicada e Tecnologia, Campus da FCUL, Campo Grande, P-1749-016 Lisboa, Portugal;
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  • Teresa S. David,

    1. Estação Florestal Nacional, Quinta do Marquês, 2780-159 Oeiras, Portugal
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  • Cathy Kurz-Besson,

    1. Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal;
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  • Jorge S. David,

    1. Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017 Lisbon, Portugal;
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  • Cristina Máguas

    1. Centro de Ecologia e Biologia Vegetal, Faculdade de Ciências, Universidade Lisboa, Campo Grande, P-1749-016 Lisbon, Portugal;
    2. ICAT-Instituto de Ciência Aplicada e Tecnologia, Campus da FCUL, Campo Grande, P-1749-016 Lisboa, Portugal;
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Author for correspondence: Christiane Werner Tel: +49-521-1065574 Fax: +49-521-1066038 Email: c.werner@uni-bielefeld.de

Summary

  • • Temporal dynamics in carbon isotope ratios of ecosystem respiration (δ13CR) were evaluated on hourly, daily and annual timescales in a Mediterranean woodland. Emphasis was given to the periods of transition from wet to dry season and vice versa, when the system turns from a net carbon sink to a source. The constancy of nocturnal δ13CR was tested.
  • • The relationship between δ13CR (determined through Keeling plots) and environmental factors was evaluated through time-lag analysis.
  • • δ13CR exhibited high annual variation (> 7). During the transition periods, δ13CR correlated significantly with factors influencing photosynthetic discrimination, soil respiration, and whole-canopy conductance. Time-lags differed between below- and above-ground variables, and between seasons. A shift in regression parameters with environmental factors indicated seasonal differences in ecosystem responsiveness (e.g. temperature acclimation). δ13CR exhibited substantial nocturnal enrichment (> 4) from dusk to dawn.
  • • These data indicate pronounced short-term dynamics in δ13CR at hourly to daily timescales and a modulated response to environmental drivers. Substantial short-term changes in nocturnal δ13CR may have important implications for the sampling protocols of nocturnal Keeling plots.

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