03789naa a2200157 a 450000100080000000500110000800800410001910000170006024501360007726000090021352030320022270000160325470000230327070000170329377303210331013147982008-09-15       2008    bl uuuu     u00u1 u    #d1 aMARGERIE, P.  aNutrients production in casts of Lumbricidae and vegetation biomass on a chalky slope of the Seine valleyba multivariate analysis.  c2008  aThe chalky slopes of the Seine valley (Upper Normandy, France) are supporting semi-natural grasslands subjects to a process of secondary succession, which leads to a mosaic of stages from short grasslands to maple woods. Soils are rendzinas, supporting high densities and biomasses of macrofauna, mainly earthworms (80 to 120 g m-²). A median stage of the succession is the Brachypodium tall grassland, which is stable when compared to other stages for at least some decades. Earthworm populations in this vegetal formation have previously been proved to exhibit spatial patterns with patches of ca. tenth of meters. In the homogeneous tall grassland, these patterns are not correlated with those of the floristic composition. We hypothesise in this work that, given that earthworms are known to provide an important source of nutrients in their casts (microsites of efficient mineralisation), the biomass of the tall grassland vegetation is correlated with earthworm cast-derived nutrients amount in the soil. A three-steps procedure was used: (i) we assessed the kinetics of nutrients (N-NO3-, N-NH4+, P-P2O5) in casts produced in the laboratory by five earthworm species (32-days incubation), and we used these results to (ii) estimate the amount of nutrients produced by real earthworm populations in field conditions and (iii) to explore the relationships between above- and belowground vegetation biomasses and cast-derived nutrients. Results obtained from step (i) are consistent with those of the literature with NH4+ and P2O5 following a roughly bell shaped curve, reaching its acme between 2 and 12 days after cast production. Phosphorus increased up to 7-fold the mean amount in soil, and NH4+ up to 2.3- fold. We found significant differences among earthworm species, with the anecic Aporrectodea giardi being the best nutrient provider in the laboratory. NO3- did not show any apparent dynamic in casts, with less than 10% variation compared to soil. The extrapolation to the field was made using a small scale study of earthworm populations and vegetation biomasses which took place on the chalky slope of Saint Adrien (64 points of 0.125 m² located on a 4 m² tall grassland surface in a square jointive design). Neither earthworm associations nor vegetation composition exhibited significant spatial pattern. A principal components analysis performed on vegetation above- and belowground biomasses and casts nutrient production estimated from earthworm biomass led to an axis 1 (26.3 % of total variance) interpreted as a size effect with all variables displaying positive values and an axis 2 (21.6 % of total variance) exhibiting a segregation between (a) aboveground biomass except the ligneous plants and (b) belowground and ligneous biomasses and nutrient production. Perspectives include the extrapolation of these small-scale results to the scale at which earthworm spatial patterns are documented, in order to quantify the potential role of earthworm populations in the kinetic of secondary succession1 aBARETTA, D.1 aAKPA-VINCESLAS, M.1 aDECAËNS, 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.