04113naa a2200157 a 450000100080000000500110000800800410001910000140006024500880007426000090016252034150017170000150358670000170360170000160361877303210363413149072008-09-22       2008    bl uuuu     u00u1 u    #d1 aHEDDE, M.  aEffects of five earthworm species on soil structure and organic matter in LUVISOLs.  c2008  aEarthworms are frequently cited as key stone soil organisms, however, their effects on soil structure stability and organic matter (OM) in macro-aggregates are mainly driven by soil type and land use. Loamy soils of the Bassin Parisien are mainly dedicated to intensive crop which have led to soil degradation. Introduction of pastures is one of the most promising practices that may restore them. The aim of this work is to quantify and compare, in laboratory experiments, the effects of 5 earthworm species on soil OM. We hypothesize that direction and magnitude of earthworm effects depend on (i) earthworm species and (ii) OM of the substrate hosting it. Five earthworm species were retained for the experiment (Aporrectodea caliginosa, Aporrectodea rosea, Allolobophora chlorotica, Aporrectodea icterica and Aporrectodea longa). The superficial soil of 3 stands were sampled in May 2006: a 30 yrs intensive crop stand (CS); a 5 yrs pasture (YP); a 46 yrs permanent pasture (PP). Soil (150 g of 2mm-sieved) was added to microcosms and moistened at field capacity at the onset of the experiment. Three replicates were set up for each treatment (species x substrate) and stored for 3 weeks in climate chambers. C-CO2 release during the experiment was estimated by the conductivity method (Heemsbergen et al., 2004). At the end of the experiment, soil was air-dried and dry-sieved at 2 mm to isolate and weight the large macro-aggregate fraction (&gt 2mm, LMA). LMA were characterized by (i) their organic matter content (loss-in-ignition at 550 °C); (ii) their stability estimated by the more desegregating test of Le Bissonnais? (1996) method and expressed as the mean weight diameter (MWD) and (iii) their organic composition assessed by Near Infrared Spectroscopy (NIRS, Antaris II Thermo electron). The C-CO2 release may result from quality or localisation of soil OM. The high C-CO2 release observed in CS-microcosms hosting earthworm can be explained by the mineralization of a labile OM pool. This hypothesis was confirmed by the decrease of OM content in LMA. On the other hand, in pasture soils, the lack of C-CO2 release increase in earthworm presence may be due to a physical or chemical protection of OM. Globally the rate of LMA production decreased with soil OM content increase. On low OM content soil, earthworms should ingest a larger amount of soil than on high OM content soil to cover the energetic needs. Aggregate structural stability produced in earthworms hosting microcosms was lower (CS soil), similar (YP soil) and higher (PP soil) than in animal-free controls. Although the factor ?species? mattered, short-term stabilisation mechanisms in those loamy soils were firstly linked to the initial soil OM content. Interpretation of NIRS spectra showed that the regular disturbance regime YP was submitted to might have maintained OM biochemical composition similar to CS one and that the composition of soil OM influence the capacities of earthworms to modify this OM composition. Biodiversity, Conservation and Sustainable Management of Soil Animals August 25 - 29, 2008 Positivo University Curitiba - Paraná - Brazil We demonstrated that earthworm short-term effects depend on both earthworm species and initial soil OM. These effects are complex and appear mainly in the more contrasted soils. Conversely, in the 5-years old pasture soil, earthworm presence has very few effects.1 aBUREAU, F.1 aCECILLON, L.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.