Litter diversity, fungal decomposers and litter decomposition under simulated stream intermittency

Authors

  • Andreas Bruder,

    Corresponding author
    1. Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland
    2. Institute of Integrative Biology (IBZ), Swiss Federal Institute of Technology (ETH), Universitätsstrasse 16, 8092 Zurich, Switzerland
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  • Eric Chauvet,

    1. Université de Toulouse; UPS, INP; EcoLab (Laboratoire écologie fonctionnelle et environnement), 118 route de Narbonne, F-31062 Toulouse Cedex 9, France
    2. CNRS, EcoLab, F-31055 Toulouse Cedex 4, France
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  • Mark O. Gessner

    1. Department of Aquatic Ecology, Eawag: Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland
    2. Institute of Integrative Biology (IBZ), Swiss Federal Institute of Technology (ETH), Universitätsstrasse 16, 8092 Zurich, Switzerland
    3. Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Alte Fischerhütte 2, 16775 Stechlin, Germany
    4. Department of Ecology, Berlin Institute of Technology (TU Berlin), Ernst-Reuter-Platz 1, 10587 Berlin, Germany
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Correspondence author. E-mail: andreas.bruder@eawag.ch

Summary

1. The drying of stream channels resulting from flow interruption is expected to increase as a consequence of climate change. Implications for aquatic organisms and processes are profound. We assessed whether riparian diversity can partially buffer against consequences of drying on fungal decomposers and leaf litter decomposition, an important ecosystem process.

2. Our central hypothesis was that during dry periods recalcitrant leaf litter with high water-holding capacity would extend the window of opportunity for microbial activity in less recalcitrant litter when both litter types are mixed, and that this would lead to a positive litter diversity effect on decomposition. To test for such interactive effects, we conducted a diversity experiment in a Mediterranean stream, in which alder and oak litter, and a mixture of both, was subjected to various drying regimes differing in intensity and timing.

3. Drying regime affected both fungal decomposers and the decomposition rate of alder litter. Effects were observed both immediately and 3 weeks after stream flow resumed. Small differences in the timing of the dry period influenced both decomposition rate and measures of fungal performance (i.e. biomass and sporulation activity). Litter mixing, in contrast, had no effect on either decomposition or fungal decomposers, although mixing increased moisture retention in alder litter as required for the mechanism hypothesized to lead to a diversity effect.

4. Given the contrasting traits of the litter types used in the experiment, our results imply that riparian tree diversity is unlikely to buffer against increased frequencies of stream flow disruption expected in the face of climate change. It appears, however, that the precise timing of dry periods and high-flow events will strongly influence the extent to which stream food webs can exploit the resources supplied by riparian vegetation in the form of leaf litter.

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