Incubation time, functional litter diversity, and habitat characteristics predict litter-mixing effects on decomposition

Authors

  • Antoine Lecerf,

    Corresponding author
    1. Université de Toulouse, UPS, INP, CNRS, EcoLab (Laboratoire d'Écologie Fonctionnelle), 29 Rue Jeanne Marvig, F-31055 Toulouse, France
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  • Guillaume Marie,

    1. Université de Toulouse, UPS, INP, CNRS, EcoLab (Laboratoire d'Écologie Fonctionnelle), 29 Rue Jeanne Marvig, F-31055 Toulouse, France
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  • John S. Kominoski,

    1. Department of Forest Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4 Canada
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    •  Present address: Odum School of Ecology, University of Georgia, Athens, Georgia 30602 USA.

  • Carri J. LeRoy,

    1. Environmental Studies Program, Evergreen State College, Olympia, Washington 98505 USA
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  • Caroline Bernadet,

    1. Université de Toulouse, UPS, INP, CNRS, EcoLab (Laboratoire d'Écologie Fonctionnelle), 29 Rue Jeanne Marvig, F-31055 Toulouse, France
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  • Christopher M. Swan

    1. Department of Geography and Environmental Systems, University of Maryland, Baltimore County, Baltimore, Maryland 21250 USA
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Abstract

Plant diversity influences many fundamental ecosystem functions, including carbon and nutrient dynamics, during litter breakdown. Mixing different litter species causes litter mixtures to lose mass at different rates than expected from component species incubated in isolation. Such nonadditive litter-mixing effects on breakdown processes often occur idiosyncratically because their direction and magnitude change with incubation time, litter species composition, and ecosystem characteristics. Taking advantage of results from 18 litter mixture experiments in streams, we examined whether the direction and magnitude of nonadditive mixing effects are randomly determined. Across 171 tested litter mixtures and 510 incubation time-by-mixture combinations, nonadditive effects on breakdown were common and on average resulted in slightly faster decomposition than expected. In addition, we found that the magnitude of nonadditive effects and the relative balance of positive and negative responses in mixtures change predictably over time, and both were related to an index of functional litter diversity and selected environmental characteristics. Based on these, it should be expected that nonadditive effects are stronger for litter mixtures made of functionally dissimilar species especially in smaller streams. Our findings demonstrate that effects of litter diversity on plant mixture breakdown are more predictable than generally thought. We further argue that the consequences of current worldwide homogenization in the composition of plant traits on carbon and nutrient dynamics could be better inferred from long-duration experiments that manipulate both functional litter diversity and ecosystem characteristics in “hotspots of biodiversity effects,” such as small streams.

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