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multi-BEF: Testing soil macrodetritivore diversity effects on litter decomposition and plant performance


The current decline of biodiversity worldwide has prompted the need to understand its impact on multiple key ecosystem functions of global relevance. Some decades of work have indeed highlighted a positive relationship between biodiversity and several ecosystem functions; however, to date, the mechanisms underlying the observed patterns are still debated. It is especially crucial to understand how functional traits determine abiotic and biotic interactions in complex, multitrophic systems. This will allow to better understand the consequences of non-random species loss or changes in community composition for future ecosystem properties, and to get scientific support for a more effective long-term conservation strategy.

The present project aims at disentangling the influence of various components of functional diversity on litter decomposition, nutrient cycling, and plant performance. By using mesocosm experiments, we manipulate the functional trait composition of macrodetritivore communities feeding on two litter species (Acer platanoides and Betula pendula), which also differ in traits determining decomposability. Three macrodetritivore species with contrasting functional traits (e.g. body size, mobility, water loss rate, feeding habit, and life history) were selected for each of three taxonomic groups: isopods (Oniscus asellus, Porcellio scaber, Armadillidium vulgare), gastropods (Cepaea nemoralis, Helicodonta obvoluta, Discus rotundatus), and earthworms (Eisenia fetida, Lumbricus rubellus, Allolobophora chlorotica).

Specifically, we test the following main hypotheses:

  1. Variation in functional traits of macrodetritivore and litter species drives complementary resource use and niche partition, and consequently enhances total litter decomposition.
  2. The effect of different macrodetritivore communities on ecosystem functioning has cascading effects through changes in soil chemical composition, subsequent plant germination and growth rate, plant-herbivore interactions (i.e. resistance against herbivores), and nutrient recycling.

“What greater stupidity can be imagined than that of calling jewels, silver, and gold 'precious,' and earth and soil 'base'?” (Galileo Galilei)

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Prior to the experiment, animals (here the isopod Oniscus asellus) are collected in the field. Photo: Yumi Bieri, WSL
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Prior to the experiment, animals (here the snail Helicodonta obvoluta) are collected in the field. Photo: Yumi Bieri, WSL
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Simone Fontana, Postdoc, verifies the identity of an isopod (Armadillidium vulgare) using a binocular connected to a camera. The same instrument is also used sometimes to measure traits on high-resolution pictures. Photo: Yumi Bieri, WSL
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Yumi Bieri, intern, prepares the boxes used for acclimating animals to the experimental conditions. Photo: Simone Fontana, WSL
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Simone Fontana, Postdoc, separates animals, litter and soil at the end of the experiment. Photo: Yumi Bieri, WSL
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Example of a mesocosm at the end of the experiment (here with the isopod Oniscus asellus). Photo: Yumi Bieri, WSL
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Patterns of litter degradation differ between taxonomic groups or even species (here the snail Cepaea nemoralis). Photo: Yumi Bieri, WSL
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A macrodetritivore species (here the earthworm Eisenia fetida) can show a different pattern of litter degradation depending on the litter species (Acer platanoides left,Betula pendula middle and right). Photo: Yumi Bieri, WSL