Sedimentologie des depots lacustres holocenes de la region de Taoudenni (Mali) : implications paleoclimatiques

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

d13C and stomatal number variability in the Cretaceous conifer.

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Coupling metal stable isotope compositions and X-ray absorption spectroscopy to study metal pathways in soil–plant systems: a mini review

International audienceExcess and limited trace metal contents in soils and plants can limit crop yields and pose a risk for the environment and human health. This mini-review reports on the emerging approach of combining X-ray absorption spectroscopy (XAS) with isotope analyses to improve the understanding of metal speciation and dynamics in soil-plant systems. In soils and their components, shifts in isotope compositions could be in some cases linked to changing metal speciation and thereby provide information on processes that control the phytoavailability of metals. In plants, the XAS-isotope approach has potential to improve the understanding of how complex interactions of metal speciation, redox processes, and membrane transport control metal uptake and translocation to edible plant parts. Yet, the XAS-isotope approach proves to be in a rather exploratory phase, and many research gaps remain. Such limitations can be overcome by methodological improvements and combining the approach with molecular biology and modelling approaches

d13C and stomatal number variability in the Cretaceous conifer Frenelopsis. Palaeogeography, Palaeoclimatology, Palaeoecology, 257, 462-473.

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Fractionation of Stable Zinc Isotopes in the Zinc Hyperaccumulator Arabidopsis halleri and Nonaccumulator Arabidopsis petraea

International audienceZn isotope fractionation may provide new insights into Zn uptake, transport and storage mechanisms in plants. It was investigated here in the Zn hyperaccumulator Arabidopsis halleri and the nonaccumulator A. petraea. Plant growth on hydroponic solution allowed us to measure the isotope fractionation between source Zn (with Zn(2+) as dominant form), shoot and root. Zn isotope mass balance yields mean isotope fractionation between plant and source Zn Delta(66)Zn(in-source) of -0.19 +/- 0.20 parts per thousand in the nonaccumulator and of -0.05 +/- 0.12 parts per thousand in-source in the hyperaccurnulator. The isotope fractionation between shoot Zn and bulk Zn incorporated (Delta(66)Zn(shoot-in)) differs between the nonaccumulator and the hyperaccumulator and is function of root-shoot translocation (as given by mass ratio between shoot Zn and bulk plant Zn). The large isotope fractionation associated with sequestration in the root (0.37 parts per thousand) points to the binding of Zn(2+) with a high affinity ligand in the root cell. We conclude that Zn stable isotopes may help to estimate underground and aerial Zn storage in plants and be useful in studying extracellular and cellular mechanisms of sequestration in the root

Fluxes and sources of particulate organic carbon in the Ganga-Brahmaputra river system

International audienceSources and fluxes of particulate organic carbon (OC) in the Ganga-Brahmaputra river system were estimated from 13C/12C ratios of bedrocks, soils, bank and suspended river sediments from a Himalayan watershed (Narayani, Nepal), and the Bangladesh floodplain. In the watershed of the Narayani, OC δ13C values for bank and suspended sediments have similar values and narrow ranges, with a mean of about −24.2‰ at the base of the Himalayas. On the Bangladesh floodplain, bank and suspended sediments are enriched in 13C (δ13C about −22.5‰) relative to those collected at the base of the Himalayas. The OC exported at the base of the Himalayan range is estimated to include about 15% from the 13C enriched C4 biomass while the C4 contribution is about 25% of the OC exported by the Ganga and Brahmaputra. A calculated total OC flux of 0.65 × 1012 molC yr−1 is exported to the ocean or trapped in the plain. In sediments of the Ganga and Brahmaputra, the clay-size fraction is depleted in 13C (<2.6‰) relative to the bulk sediment. Possible explanations are that either the organic matter associated with clays is largely inherited from the Himalayan watersheds, or, and considered more likely, the clays and coarser sediments sample different OC pools, possibly with different ages (the growth of C4 crops has dramatically increased since the mid twentieth century), on the floodplain. The OC budget of the actual Ganga-Brahmaputra system is broadly comparable to that derived from the Quaternary sediments of the Bengal fan that represents about 10% of the global OC contribution to the continental margins

Changes of Cadmium Storage Forms and Isotope Ratios in Rice During Grain Filling

International audienceRice poses a major source of the toxic contaminant cadmium (Cd) for humans. Here, we elucidated the role of Cd storage forms (i.e., the chemical Cd speciation) on the dynamics of Cd within rice. In a pot trial, we grew rice on a Cd-contaminated soil in upland conditions and sampled roots and shoots parts at flowering and maturity. Cd concentrations, isotope ratios, Cd speciation (X-ray absorption spectroscopy), and micronutrient concentrations were analyzed. During grain filling, Cd and preferentially light Cd isotopes were strongly retained in roots where the Cd storage form did not change (Cd bound to thiols, Cd–S = 100%). In the same period, no net change of Cd mass occurred in roots and shoots, and the shoots became enriched in heavy isotopes (Δ 114/110 Cd maturity–flowering = 0.14 ± 0.04‰). These results are consistent with a sequestration of Cd in root vacuoles that includes strong binding of Cd to thiol containing ligands that favor light isotopes, with a small fraction of Cd strongly enriched in heavy isotopes being transferred to shoots during grain filling. The Cd speciation in the shoots changed from predominantly Cd–S (72%) to Cd bound to O ligands (Cd–O, 80%) during grain filling. Cd–O may represent Cd binding to organic acids in vacuoles and/or binding to cell walls in the apoplast. Despite this change of ligands, which was attributed to plant senescence, Cd was largely immobile in the shoots since only 0.77% of Cd in the shoots were transferred into the grains. Thus, both storage forms (Cd–S and Cd–O) contributed to the retention of Cd in the straw. Cd was mainly bound to S in nodes I and grains (Cd–S &gt; 84%), and these organs were strongly enriched in heavy isotopes compared to straw (Δ 114/110 Cd grains/nodes– straw = 0.66–0.72‰) and flag leaves (Δ 114/110 Cd grains/nodes–flag leaves = 0.49–0.52‰). Hence, xylem to phloem transfer in the node favors heavy isotopes, and the Cd–S form may persist during the transfer of Cd from node to grain. This study highlights the importance of Cd storage forms during its journey to grain and potentially into the food chain

Insights into preservation of fossil plant cuticles using thermally assisted hydrolysis methylation.

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Rhine’s floods during roman antiquity. Geoarchaeology of the Oedenburg Gallo-Roman site (France).

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