Functional diversity of photosynthesis during drought in a model tropical rainforest – the contributions of leaf area, photosynthetic electron transport and stomatal conductance to reduction in net ecosystem carbon exchange

Authors

  • U. RASCHER,

    Corresponding author
    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
    2. Institute of Chemistry and Dynamics of the Geosphere ICG-III: Phytosphere, Forschungszentrum Jülich, Stetternicher Forst, 52425 Jülich, Germany,
    3. Earth Institute, Columbia University, 535 West 116th Street, New York, NY 10027, USA,
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      Institute of Chemistry and Dynamics of the Geosphere ICG-III: Phytosphere, Forschungszentrum Jülich, Stetternicher Forst, 52425 Jülich, Germany.

  • E. G. BOBICH,

    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
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      These co-authors contributed equally to the manuscript.

    • Department of Ecology and Evolutionary Biology, University of Arizona, PO Box 210088, Tucson, AZ 85721, USA.

  • G. H. LIN,

    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
    2. Department of Global Ecology, Carnegie Institution of Washington, 260 Panama St., Palo Alto, CA 94305–1297, USA,
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    • *

      These co-authors contributed equally to the manuscript.

    • Laboratory of Quantitative Vegetation Ecology and Center for Plant Ecology and Biodiversity Conservation, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.

  • A. WALTER,

    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
    2. Institute of Chemistry and Dynamics of the Geosphere ICG-III: Phytosphere, Forschungszentrum Jülich, Stetternicher Forst, 52425 Jülich, Germany,
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    • *

      These co-authors contributed equally to the manuscript.

  • T. MORRIS,

    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
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  • M. NAUMANN,

    1. Darmstadt University of Technology, Institute of Botany, Schnittspahnstr. 3–5, 64287 Darmstadt, Germany,
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  • C. J. NICHOL,

    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
    2. School of GeoSciences, Darwin Building, Kings Buildings, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JU, Scotland, UK and
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  • D. PIERCE,

    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
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  • K. BIL,

    1. Biosphere 2 Center, Columbia University, P.O. Box 689, Oracle, AZ 85623, USA,
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  • V. KUDEYAROV,

    1. Institute of Physicochemical and Biological Problems of Soil Science. Russian Academy of Science, Pushchino, Moscow Region, 142290, Russia
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  • J. A. BERRY

    1. Department of Global Ecology, Carnegie Institution of Washington, 260 Panama St., Palo Alto, CA 94305–1297, USA,
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Uwe Rascher. Fax: + 49 (2461) 61 2492; e-mail: u.rascher@fz-juelich.de

ABSTRACT

The tropical rainforest mesocosm within the Biosphere 2 Laboratory, a model system of some 110 species developed over 12 years under controlled environmental conditions, has been subjected to a series of comparable drought experiments during 2000–2002. In each study, the mesocosm was subjected to a 4–6 week drought, with well-defined rainfall events before and after the treatment. Ecosystem CO2 uptake rate (Aeco) declined 32% in response to the drought, with changes occurring within days and being reversible within weeks, even though the deeper soil layers did not become significantly drier and leaf-level water status of most large trees was not greatly affected. The reduced Aeco during the drought reflected both morphological and physiological responses. It is estimated that the drought-induced 32% reduction of Aeco has three principal components: (1) leaf fall increased two-fold whereas leaf expansion growth of some canopy dominants declined to 60%, leading to a 10% decrease in foliage coverage of the canopy. This might be the main reason for the persistent reduction of Aeco after rewatering. (2) The maximum photosynthetic electron transport rate at high light intensities in remaining leaves was reduced to 71% for three of the four species measured, even though no chronic photo-inhibition occurred. (3) Stomata closed, leading to a reduced ecosystem water conductance to water vapour (33% of pre-drought values), which not only reduced ecosystem carbon uptake rate, but may also have implications for water and energy budgets of tropical ecosystems. Additionally, individual rainforest trees responded differently, expressing different levels of stress and stress avoiding mechanisms. This functional diversity renders the individual response heterogeneous and has fundamental implications to scale leaf level responses to ecosystem dynamics.

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