Review

Animals and the zoogeochemistry of the carbon cycle

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Science  07 Dec 2018:
Vol. 362, Issue 6419, eaar3213
DOI: 10.1126/science.aar3213

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  • Herbivory, plant gas exchange and wetland carbon cycling
    • Robert Scott Winton, Postdoctoral Researcher, ETH Zurich
    • Other Contributors:
      • Curtis J Richardson, Professor of Resource Ecology, Duke University

    In their paper “Animals and the zoogeochemistry of the carbon cycle,” O. Schmitz et al. review the mechanisms of animal influence on carbon cycling. The authors fail to recognize the process of gas exchange by wetland plants (2), its importance for methane (CH4) emission (3), and three recent experiments from three continents documenting the capacity for herbivores to strongly alter rates of wetland CH4 emission by modifying plant gas exchange. Dingemans et al., 2011 document a five-fold increase in CH4 emissions from stands of Common Reed (Phragmites australis) grazed by graylag geese (Anser anser); Petruzzella et al., 2015 find a 3.5-fold increase in CH4 from rush stems (Eleocharis equisetoides) damaged by herbivorous grasshoppers (Stenacris sp.); and Winton and Richardson, 2017 find that wintering flocks of Tundra Swan (Cygnus colombianus) and mixed duck species grazing on dormant rush roots and tubers delay the re-emergence of rush stems (Eleocharis quandrangulata), preventing the transport of oxygen to wetland soils and increasing CH4 emission by 230%.
    Without these important studies of wetland herbivory, O. Schmitz et al.’s assemblage of 14 experiment-based estimates of the effects of wild animals on carbon cycling is incomplete and misleading. Their review gives the false impression that the effects of herbivory are relatively minor in marsh ecosystems or when the grazers are birds (e.g. Elschot et al., 2015). On the contrary, available evidence indicates that...

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    Competing Interests: None declared.