Pierre Margerie

Protein N-glycosylation is similar in the moss Physcomitrella patens and in higher plants

We have investigated the structure of glycans N-linked to the proteins of the moss Physcomitrella patens. The structural elucidation was carried out by western blotting using antibodies specific for N-glycan epitopes and by analysis of N-linked glycans enzymatically released from a total protein extract by combination of MALDI–TOF and MALDI–PSD mass spectrometry analysis. Nineteen N-linked oligosaccharides were characterised ranging from high-mannose-type and truncated paucimannosidic-type to complex-type N-glycans harbouring core-xylose, core-α(1,3)-fucose and Lewisa, as previously described for proteins from higher plants. This demonstrates that the processing of N-linked glycans, as well as the specificity of glycosidases and glycosyltransferases involved in this processing, are highly conserved between P. patens and higher plants. As a consequence, P. patens appears to be a new promising model organism for the investigation of the biological significance of protein N-glycosylation in the plant kingdom, taking advantage of the potential for gene targeting in this moss.

Earthworm communities in a wet agricultural landscape of the Seine Valley (Upper Normandy, France)

This study was carried out to describe the driving factors responsible for earthworm community structure in a wet landscape of the Seine Valley (Upper Normandy, France). Fifteen plots were selected along a 1300 m transect, representing the main agroecosystems (i.e. wooded systems, orchards, grasslands, crops) and soil types (i.e. FLUVIOSOL, REDUCTISOL, HISTOSOL and COLLUVIOSOL) in the area. Five samples were taken in each plot using a combination of formalin extraction and hand sorting. Earthworms were identified to species level, counted and weighed. Communities responded markedly to agricultural intensification. The highest mean biomass, density and diversity were observed in the medium intensity systems (up to 119.7 g fresh weight m - 2 , 309.3 ind m - 2 , 7.2 sp m - 2 in orchards, respectively). Soil type only had significant effects on community composition and diversity. A principal component analysis was performed with broad descriptive parameters of communities. The first two axes accounted for 50.8 % of the total inertia. It separated wooded systems (endogeics and epigeics dominant, low total density, biomass and diversity) from orchards and grasslands (endogeics and/or anecics dominant, high diversity and density) and crops (low diversity, biomass and density). The ordination of plots according to soil type segregated low-lying soils (endogeics and epigeics dominant, low diversity, high density) from better-drained soils (anecics dominant, high density and diversity). Agricultural activities and natural soil heterogeneity are environmental filters that shape community composition and structure at the landscape scale. In the present study, soil type mainly determined earthworm community composition at the scale of soil type patches, while agricultural practices had a stronger impact on community structure at the scale of the agricultural plot.

Effects of tree canopy composition on earthworms and other macro-invertebrates in beech forests of Upper Normandy (France)

Summary The effect of canopy composition on soil macro-invertebrate communities in two deciduous temperate forests: a pure beech (Fagus sylvatica L.) and a mixed beech-hornbeam (Carpinus betulus L.) stand was investigated. The initial hypothesis was that heterogeneity of trophic resources within the mixed stand might increase diversity and heterogeneity of soil macro-invertebrate communities at stand level. The macrofauna was sampled in autumn and spring by hand sorting 121 (25 × 25 × 30 cm) soil monoliths regularly distributed within each stand. Earthworms were identified to species level while the remaining macro-invertebrates were identified to family level. Results were analysed by univariate and multivariate (PCA) statistical tools as well as a geostatistical tool. Few differences were observed when comparing the total macro-invertebrate density between sites and dates. In contrast, significant patterns were found for several taxonomic or trophic groups taken separately (e.g. Lumbricidae, detritivore and predator densities were significantly higher in the pure beech stand (PS). The first and the third PCA axes respectively revealed a site and a season effect while the second axis revealed a spatial segregation within the detritivore group as it distinguished high densities of Lumbricidae from those of Isopoda and Diplopoda. The variance of record scores on this axis measured for each site and date revealed that spatial variability of soil macrofauna communities was greater for PS on both dates than for MS. Semi-variance analysis performed on record coordinates on the second axis of the PCA revealed that only macro-invertebrate communities sampled under the pure stand in autumn were spatially structured (autocorrelation range about 32 m). These results do not support the general agreement that resource diversity and patchiness increases soil fauna biodiversity and heterogeneity.

Spatial distribution of earthworm species assemblages in a chalky slope of the Seine Valley (Normandy, France)

The aim of this study was to characterize the spatial distribution of earthworm species assemblages on a chalky slope of the Seine Valley (Upper Normandy, France), with contrasting vegetation cover representing the different stages of a typical post-pastoral secondary succession. Samples were hand sorted in a spatially explicit design consisting of a regular grid. A Principal Component Analysis was performed to identify species associations. Maps of the factorial coordinates of sample points together with geostatistical analysis were used to describe the spatial structure of the assemblages. The first axis of the PCA opposed points with high density to others with low. The resulting spatial structure was significant. The second axis opposed points where species assemblages were dominated either by an endogeic (Allolobophora chlorotica), an anecic (Aporrectodea longa) and an epigeic species (Lumbricus castaneus) to others dominated by two endogeics (Aporrectodea rosea and Octolasium cyaneum). A significant spatial structure was detected, with alternating patches characterised by one species assemblage or the other. The location of these structures did not seem to be clearly associated with a specific vegetation type. These results revealed a complex determinism of species co-occurrence at small spatial scale.

Soil detritivore macro-invertebrate assemblages throughout a managed beech rotation

This work addresses the driving factors responsible for patterns in the detritivore macrofaunal communities of a managed beechwood chronosequence (28 to 197 years old, Normandy, France). We investigated the variation patterns of density, biomass and diversities of detritivore macrofauna throughout this rotation. Multivariate analyses were carried out to identify the main covariation patterns between species and some properties of their physical environment, and to describe the main ecological gradients constraining the macro-invertebrate community assembly. A total of 6 earthworm, 6 woodlouse and 7 millipede species were found in the whole data set. Density, biomass and diversity were profoundly influenced by forest ageing, mainly because of variation in humic epipedon spatial variability. Three groups of species were identified according to their environmental requirements. Some hypotheses regarding the external (related to management practices) or internal (related to inter-specific interactions) assembly rules behind species assemblages are proposed, an approach which has rarely been used in soil ecology. Finally, the impact of forestry practices on soil functioning through their impact on detritivore macro-invertebrate communities is discussed.RésuméCe travail a pour but d’identifier les facteurs responsables des schémas de variation des communautés de la macrofaune detritivore d’une chronoséquence (28 à 197 ans) de futaie régulière de hêtre (Normandie, France). Les modèles de variation de la densité, la biomasse et la diversité ont été recherchés. Les modèles de covariation entre les espèces et certaines propriétés physiques du milieu ainsi que les gradients écologiques qui contraignent les assemblages de macro-détritivores ont été décrits à l’aide d’analyses multivariées. En tout, 6 espèces de vers de terre, 6 espèces d’isopodes et 7 espèces de diplopodes ont été identifiées. La maturation du peuplement de hêtre, principalement par les modifications de l’épisolum humifère, influence fortement les densité, biomasse et diversité. Trois groupes d’espèces sont identifiés sur la base de leurs exigences environnementales. Quelques hypothèses sont proposées quant aux règles externes (liées aux pratiques sylvicoles) et internes (liées aux relations interspéciques) qui contraignent la composition des assemblages d’espèces, cette approche ayant jusqu’à présent été peu utilisée en écologie du sol. Enfin, l’impact des pratiques sylvicoles sur le fonctionnement du sol, au travers de leur impact sur les communautés de macro-détritivores, est discuté.