04745naa a2200157 a 450000100080000000500110000800800410001910000140006024501240007426000090019852040120020770000150421970000160423470000160425077303210426613149062008-09-22       2008    bl uuuu     u00u1 u    #d1 aHEDDE, M.  aMechanisms responsible for diversity-leaf degradation relationship within litter invertebrate experimental assemblages.  c2008  aDespite the great interest concerning the relationship between species diversity and ecosystem functioning, there low knowledge as to how the diversity of detritivore macro-invertebrate influences the decomposition of soil organic matter. The aim of this paper was twofold. First, what is the more relevant measure of diversity to estimate species assemblage effect on a given function? Second, what are the mechanisms underlying the observed BD-EF patterns? To answer these questions, we explored the relationship between small experimental communities of litter macro-detritivore invertebrates and selected indicators of organic matter degradation. Four detritivore macro-invertebrate species were selected: a woodlouse (Oniscus asellus), an earthworm (Dendrodrilus rubidus) and two millipedes (Glomeris marginata and Cylindroiulus latestriatus). All mixtures from one to four species were made (3 replicates). Invertebrates were added to microcosms with partially decayed beech leaves. Microcosms were stored for 3 weeks in climate chambers. Performances on leaf mass loss and C-CO2 release were measured. Assemblage diversity was measured through (i) species richness (SR), (ii) morphological dissimilarity (MD) and (iii) functional dissimilarity (FD). Dissimilarities were assessed by Euclidean distances between species trait coordinates in a multivariate space. Morphological traits were chosen among morphological attributes related to resource foraging and litter fragmentation. Functional traits were linked to leaf degradation abilities. The calculation of net diversity effects and transgressive overyielding allowed discriminating between negative, neutral and positive interspecific interactions responsible for observed patterns. Performances of macro-invertebrate assemblages on beech leaf degradation process appeared to be related to FD rather than to MD or SR. While it has been documented for plant productivity, only one experiment showed it for soil process. We can advocate that functional equivalence within mixture of species belonging to a same trophic group limits its performance on leaf degradation processes. Saturation in process rates occurred after more than SR was greater than one species which should have reinforced the idea that a significant impact of soil organisms occurred on decomposition and nutrient cycling at low level of SR, leading to misunderstanding of BD-EF relationship. Performances of species mixtures were due to negative, neutral or positive interspecific relationships. Species complementarity explained both leaf mass loss and C mineralisation performances of D. rubidus-O. asellus and C. latestriatus-O. asellus mixtures. We can argue that this complementarity was likely to be related to facilitation rather than to niche differentiation since substrate heterogeneity has been minimized in our experimental design. Conversely, performances of C. latestriatus-D. rubidus associations were due to neutral interspecific relationships. This may reveal that these two species fed on different part of decaying leaves without interactions. Underlying mechanisms of performances for all other mixtures differed between leaf degradation indicators (leaf mass loss and C-CO2 release). This is consistent Biodiversity, Conservation and Sustainable Management of Soil Animals August 25 - 29, 2008 Positivo University Curitiba - Paraná - Brazil with the idea that mechanisms of species performance may differ, for a given mixture, according to process. In our work, we used statistics to measure the degree of species dissimilarity instead of grouping species a priori based on similarity in morphology, life-history, and/or function. Exploring the BD-EF relationships is related to the question whether equivalence exists between species performances. This idea is specifically embodied in the concept of ?functional groups?. Our work and that of others suggests that when we simplify the world by ignoring species identities, that cost is often too great.1 aBUREAU, F.1 aCHAUVAT, M.1 aDECAENS, T.  tIn: INTERNATIONAL COLLOQUIUM ON SOIL ZOOLOGY, 15; INTERNATIONAL COLLOQUIUM ON APTERYGOTA, 12., 2008, Curitiba. Biodiversity, conservation and sustainabele management of soil animal: abstracts. Colombo: Embrapa Florestas. Editors: George Gardner Brown; Klaus Dieter Sautter; Renato Marques; Amarildo Pasini. 1 CD-ROM.