The effect of elevated atmospheric CO2 and drought on sources and sinks of isoprene in a temperate and tropical rainforest mesocosm

Authors

  • Emiliano Pegoraro,

    1. Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA,
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    • 1Present address: School of GeoSciences, University of Edinburgh, Darwin Building, Mayfield Road, Edinburgh EH9 3JU, UK.

  • Leif Abrell,

    1. Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA,
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    • 2Present address: Department of Chemistry, University of Arizona, 1306 E. University Blvd., Tucson, AZ 85721, USA.

  • Joost Van Haren,

    1. Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA,
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    • 3Present address: USDA-ARS Southwest Watershed Research Center, 2000 E. Allen Road, Tucson, AZ 85719, USA.

  • Greg Barron-Gafford,

    1. Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA,
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    • 4Present address: Department of Ecology and Environmental Biology, University of Arizona, Tucson AZ 85721, USA.

  • Katherine Ann Grieve,

    1. Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA,
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    • 5Present address: Quantitative Ecology and Resource Management, University of Washington, PO Box 352182, Seattle, WA 98195, USA.

  • Yadvinder Malhi,

    1. School of Geography and the Environment, University of Oxford, UK,
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  • Ramesh Murthy,

    1. Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA,
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    • 6Present address: 1691 W. Winchester Way, Chandler, AZ 85248, USA.

  • Guanghui Lin

    1. Biosphere 2 Center, Columbia University, Oracle, AZ 85623, USA,
    2. Key Laboratory of Quantitative Vegetation, Institute of Botany, The Chinese Academy of Science, 20 Nanxincun, Xiangshan, Beijing 100093, China
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    • 7Present address: Department of Global Ecology, Carnegie Institution of Washington, Stanford, CA 94305, USA.


Emiliano Pegoraro, e-mail: e.pegoraro@ed.ac.uk

Abstract

Isoprene is the most abundant volatile hydrocarbon emitted by many tree species and has a major impact on tropospheric chemistry, leading to formation of pollutants and enhancing the lifetime of methane, a powerful greenhouse gas. Reliable estimates of global isoprene emission from different ecosystems demand a clear understanding of the processes of both production and consumption. Although the biochemistry of isoprene production has been studied extensively and environmental controls over its emission are relatively well known, the study of isoprene consumption in soil has been largely neglected.

Here, we present results on the production and consumption of isoprene studied by measuring the following different components: (1) leaf and soil and (2) at the whole ecosystem level in two distinct enclosed ultraviolet light-depleted mesocosms at the Biosphere 2 facility: a cottonwood plantation with trees grown at ambient and elevated atmospheric CO2 concentrations and a tropical rainforest, under well watered and drought conditions. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter-free soil of the agriforest stands showed no significant response to different CO2 treatments, while isoprene production was strongly depressed by elevated atmospheric CO2 concentrations. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. We conclude that soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget. More studies investigating the capacity of soils to uptake isoprene in natural conditions are clearly needed.

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