Comparaison de plusieurs indices de diversité dans l’étude d’un peuplement de Mantes

The biological diversity of praying Mantids has been analysed to illustrate some classical indices between stability and diversity on the one hand and the numbers of individuals and species on the other. A good description of the Mantid communities can be reached by using only two parameters : the « a », of Fischer for specific richness and the « E » of Margalef for interspecific relations

Beating of hemp bast fibres: an examination of a hydro-mechanical treatment on chemical, structural, and nanomechanical property evolutions

In this study, a gradually increased hydro-mechanical treatments duration were applied to native hemp bast fibres with a traditional pulp and paper beating device (laboratory Valley beater). There is often a trade-off between the treatment applied to the fibres and the effect on their integrity. The multimodal analysis provided an understanding of the beating impact on the fibres at multiple scales and the experimental design made it possible to distinguish the effects of hydro- and hydro-mechanical treatment. Porosity analyses showed that beating treatment doubled the macroporosity and possibly reduced nanoporosity between the cellulose microfibrils. The beating irregularly extracted the amorphous components known to be preferentially located in the middle lamellae and the primary cell walls rather than in the secondary walls, the overall increasing the crystallinity of cellulose from 49.3 % to 59.1 %, but a non-significant change in the indentation moduli of the cell wall was observed. In addition, beating treatments with two distinct mechanical severities showed a disorganization of the cellulose conformation, which significant dropped the indention moduli by 11.2 GPa and 8.4 GPa for 10 and 20 minutes of Valley beater hydro-mechanical treatment, respectively, compared to hydro-treated hemp fibres (16.6 GPa). Pearson’s correlation coefficients between physicochemical features and the final indentation moduli were calculated. Strong positive correlations were highlighted between the cellulose crystallinity and rhamnose, galactose and mannose as non-cellulosic polysaccharide components of the cell wall

Vermiculite with hydroxy-aluminium interlayer and kaolinite formation in a subtropical sandy soil from south Brazil

International audienceThe purpose of this study was to investigate the clay mineral phases in a Rhodic Acrisol soil and subsequently discuss their evolution in substropical conditions. Prairie and forest soil profiles were sampled and clay fractions of the parent material and soil horizons analyzed by X-ray diffraction (XRD) at the Federal University of Santa Maria, Rio Grande do Sul-Brazil. The XRD results show the presence of interstratified kaolinite-smectite as well as illite in the parent material. These minerals were also found in the soil samples but with two new phases: hydroxy-aluminium interlayered vermiculite (HIV), which showed incomplete collapse with treatment at 550°C, and a newly formed kaolinite (d = 7,17 A). Under a subtropical climate and a sandy lithology, HIV and kaolinite appear to be a result of a specific pedogenic clay formation, in relation with the natural vegetation. Originally under the prairie area, the intensity of the weathering processes were weak (within 2:1 clay minerals), as only small quantities of kaolinite and Fe oxides, and no evidence of gibbsite, were found

Clay mineral dissolution following intensive cultivation in a tropical sandy soil

International audienceSandy soils of Northeast Thailand are predisposed to high acidification rates due to leaching and the export of alkalinity is associated with crop removal in these intensive cropping systems. Despite significant acid release, soil pH generally remains stable at a threshold value of around 4.0. Low organic matter content and the absence of weatherable primary minerals would suggest that clay mineral dissolution is responsible for the high degree of buffering commonly observed in these soils. The objective of this study was to investigate changes in nature and organisation of clay minerals following intensive cultivation in a typical sandy soil from Northeast Thailand. Surface soils were sampled under a forest (FS) and an adjacent area cultivated for 50 years (CS); they were compared with parent material sampled at 3.5 meter depth (PM) with the aim of characterising the evolution of clay minerals through pedogenesis and cultivation. The proportion of small particles (mode 0.1 µm) decreased according to pedogenesis – from parent material to soil, and land use – from forest to crop. Under the cultivated and forest soils, particles of kaolinite appeared to be very small (0.02-0.10 µm), poorly crystallised and eroded, often organised as aggregates of 1-2 µm. Expandable 2:1 clay minerals were associated with kaolinite. Chemical data of individual particles revealed that kaolinite contained iron and that expandable 2:1 clay minerals were smectite, vermiculite and mixed-layer illite/smectite. X-ray diffraction patterns of <2 µm-fractions indicated that kaolinite was the main phase, 78%, 88% and 88% in CS, FS and PM respectively, smectite being a minor phase with 20%, 6% and 12% respectively. Our results suggest that the dissolution of kaolinite was accelerated in cultivated system (CS), with a correlative neoformation of smectite, which buffers potential declines in soil pH