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The chemical composition of the wood reflects the composition of the soil over which the corresponding tree has developed. Multi-elemental and isotopic signatures, which are characteristic of the soil and underlying rock substrates, are potentially powerful tools for determining wood provenance. These tracers are of special interest for charred archaeological wood because they circumvent some limitations of dendrochronological provenancing linked to tree-ring loss. However, thermal degradation may introduce a significant bias in wood chemical and isotopic analyses. This experimental study focused on the effects of carbonization temperature on three geochemical wood markers: elemental signatures and isotopic signatures of strontium and neodymium (86Sr/87Sr and 143Nd/144Nd, respectively). Wood specimens from a variety of oak trees and stand locations were pyrolyzed at four temperatures (ranging from 200°C to 800°C) and analyzed using ICP-MS and μ-XRF (X-ray fluorescence) spectroscopy for elemental composition and with multiple collection ICP-MS (MC-ICP-MS) for strontium (Sr) and neodymium (Nd) isotope composition. The concentration of mineral nutrients generally increased with temperature, but the magnitude of the enrichment depended on the element, wood compartment (sapwood vs. heartwood), and geological substrate. The concentrations of rubidium, strontium, manganese, magnesium, potassium, and, to a lesser extent, calcium, were minimally affected by temperature, wood compartment, and substrate. The ratios between the concentrations of these elements, as well as the 86Sr/87Sr and 143Nd/144Nd isotope ratios, were stable over the entire temperature range. However, only 86Sr/87Sr and selected elemental ratios (calcium or magnesium normalized to manganese) were successful for site discrimination. Therefore, our multi-tracer approach provides promising new information to determine the provenance of charred archaeological wood.

Studies on the provenance of wood for shipbuilding contribute widely to the fields of archaeology, anthropology, environmental history, cultural geography, and palaeoclimatology. The development of reference datasets to determine the date and provenance of shipwreck timbers is therefore a paramount undertaking. Here we compile and present recent advances in the development of tree-ring chronologies, stable strontium isotope ratios and chemical biomarkers aimed to determine the date and provenance of Iberian shipwreck timbers. A set of oak and pine tree-ring chronologies have been developed from living trees covering the past 500 and 800 years, respectively, and have served to confirm the provenance of the wood used in an 18th-century Spanish ship of the Royal Navy. Stable strontium isotopic signatures have been obtained from soil and living trees at 26 sites throughout the Iberian Peninsula, providing a climate-independent geochemical network to source the origin of historic timbers. However, retrieving the original isotopic signature from waterlogged samples remains unsuccessful, stressing the need to develop effective protocols to separate the seawater signal from the original strontium isotope ratios in the wood. Analyses of organic compounds in wood of living trees have proven suitable to discriminate species and provenances, but results on shipwreck timbers are inconclusive and should be further explored. Our regional approach has the potential to be expanded to other areas and archaeological timbers from different periods throughout the Anthropocene. We highlight the strengths and weaknesses of the techniques presented when applied to waterlogged wood, propose GIS tools to interpret and visualize combined results, and stress the need to expand these type of reference datasets to allow for multiproxy dendroprovenancing approaches This research, and particularly authors MDD, SR, MT, FH, LA, and PG, was funded by the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP72007-2013) under REA grant agreement no. PITN-GA 2013-607545. MDD has also received funding from the Dutch Research Council [Nederlandse Organisatie voor Wetenschappelijk Onderzoek, grant number 016.Veni.195.502] SI

Phlogopite weathering experiments were carried out under aerobic conditions in a closed system to study Mg isotopic fractionation during the dissolution and processes involved in the presence of bacterial strains. Four different bacterial strains with different metabolisms were chosen. Biotic experiments were performed in batch reactors at 24 °C for 12 days. In parallel, abiotic phlogopite weathering experiments were also performed using organic and nitric acids. Citric and gluconic acids were used to model the effects of chelating agents produced by bacteria, and nitric acid was used to model the effects of acidifying agents. The results indicate that both decreases in pH and the production of metabolites during heterotrophic bacterial activities significantly accelerate the release of Mg and Si in solution. Also, at a given pH, the fraction of elements released in solution is greater in the presence of bacteria or citric acid compared to that released in the presence of nitric and gluconic acids. Magnesium isotopic analyses indicate that the solutions obtained using nitric acid and acidifying bacterial strains display, on average, δ26Mg values that are close to or slightly heavier (by 0.4‰) than those of fresh phlogopite (−1.2‰ ± 0.08). In contrast, in experiments performed with citric acid, the Mg leached into solution is slightly enriched in light isotopes by −0.3‰ relative to the initial phlogopite, while its binding to organics is expected to be related to its preferential enrichment in heavy isotopes. Despite its small range of variations, the δ26Mg values of solutions vary inversely with pH, thus suggesting that secondary phases preferentially enriched in 26Mg at the highest pH values may play a key role.

International audience; AbstractKey messageAggregation was studied in two acidic forest soils (NE France) to investigate the potential link between available Ca and Mg content and soil aggregate size distribution and properties. Clay content influenced the aggregation status while clay mineralogy influenced aggregate stability and dynamics. Aggregation status and reactivity of soil components contributed to the difference of exchangeable Ca and Mg content in topsoil between the two sites.ContextThough nutrient fluxes are important to define forest soil chemical fertility, the quantification of nutrient reservoirs in the soils and their availability to tree uptake is essential. A thorough understanding of nutrient availability requires an investigation of nutrient location and distribution in the soil solid phase.AimsThe general aim was to investigate the potential link between available Ca and Mg content and soil aggregate size distribution and their properties (chemical, physical, mineralogical).MethodsSoil aggregates were separated according to three size classes (200–2000 μm; 50–200 μm

Different approaches are used to study wood provenance, but most of them are based on tracers in wood that are generally controlled by climatic factors. The strontium isotopic ratio 87 Sr/ 86 Sr in trees and soils is related to the signature of the local bedrock. Despite being used in diverse archaeological studies, Sr isotopes have rarely been used to trace the provenance of archaeological wood and especially wood from shipwrecks. In addition, recent analytical advances have allowed the detection of mass-dependent fractionation of Sr isotopes during biogeochemical processes, as reflected in the variation of δ 88/86 Sr values between different environmental materials. The δ 88/86 Sr values could be used in conjunction with the 87 Sr/ 86 Sr isotope ratio to improve constraints on the sources of Sr in the archaeological materials being studied. This paper discusses the potential and limitations of using both of these Sr isotope ratios to trace the provenance of wood from shipwrecks. We review the 87 Sr/ 86 Sr and δ 88/86 Sr variations in rocks, waters, soils, plants and other living organisms and discuss how to determine the local Sr isotopic signature of potential sites. We also compile a list of known wood post mortem modifications in seawater. Possible implications in terms of the modification of the original Sr isotope ratios of wood during storage in seawater are illustrated through preliminary observations. This paper points out some limitations and perspectives for using Sr isotopes in provenancing wood from shipwrecks, and suggests future research to test and apply this approach for tracing the origin of archaeological wood.

International audience; This study investigates the potential of Mg isotopes as tracers of biogeochemical processes in a small-forested catchment located on sandstones extremely poor in Mg-bearing minerals. The average delta Mg-26 is -0.63 +/- 0.12 parts per thousand and 0 +/- 0.14 parts per thousand for local rainwater and bedrock, respectively. From the C horizon to the upper eluvial (E) horizon, soil delta Mg-26 (from 0.0 +/- 0.14 parts per thousand to 0.25 +/- 0.14 parts per thousand) is close to the bedrock value, while more than 70% of Mg is lost, suggesting a small isotopic shift during illite dissolution. The surface soil horizon (A(h)) delta Mg-26 is close to plant delta Mg-26, and especially to the grass delta Mg-26 value (-0.49 parts per thousand). The bulk delta Mg-26 of trees and grass (-0.32 parts per thousand and -0.41 parts per thousand, respectively) are higher than the average delta Mg-26 values of the soil exchangeable fraction (-0.92 parts per thousand to -0.42 parts per thousand), and of rainwater (-0.65 parts per thousand). Within plants, roots are enriched in heavy isotopes, whereas light isotopes are preferentially translocated and stored in the above ground parts. In Norway spruce, the older needles, forming the annual litterfall, are isotopically lighter and strongly depleted in Mg compared to more recent needles. Soil solution delta Mg-26 shifts seasonally, from low values, lower than rainwater and close to litterfall during a high rainfall period in spring, to higher values, close to soil delta Mg-26 in dryer periods of winter or summer. At the watershed scale, streamwater delta Mg-26 varies between -0.85 perpendicular to 0.14 parts per thousand and -0.08 perpendicular to 0.14 parts per thousand and delta Mg-26 values decrease linearly with discharge. The high streamwater delta Mg-26 at low flow, close to bedrock delta Mg-26, most likely reflects dissolution processes in the deep saprolite in relation to the very long water residence time. Conversely, we suggest that low stream level delta Mg-26 values are at least partly related to the contribution of surface flows from wet areas. Using a simple mass and isotopic balance approach, we compute that mineral dissolution rates in the soil (0.35 kg Mg ha(-1) year(-1)) presently compensate for Mg losses from the soil. (C) 2012 Elsevier Ltd. All rights reserved.

This study presents a chemical protocol for the separation of Mg that is particularly adapted to alkali-rich samples (granite, soil, plants). This protocol was based on a combination of two pre-existing methods: transition metals were first removed from the sample using an AG-MP1 anion-exchange resin, followed by the separation of alkalis (Na, K) and bivalent cations (Ca2+, Mn2+ and Sr2+) using a AG50W-X12 cation-exchange resin. This procedure allowed Mg recovery of ∼ 10 0 ± 8%. The [Σcations]/[Mg] molar ratios in all of the final Mg fractions were lower than 0.05. The Mg isotope ratios of eleven reference materials were analysed using two different MC-ICP-MS instruments (Isoprobe and Nu Plasma). The long-term reproducibility, assessed by repeated measurements of Mg standard solutions and natural reference materials, was 0.14‰. The basalt (BE-N), limestone (Cal-S) and seawater (BCR-403) reference materials analysed in this study yielded δ26Mg mean values of −0.28 ± 0.08‰, −4.37 ± 0.11‰ and −0.89 ± 0.10‰ respectively, in agreement with published data. The two continental rocks analysed, diorite (DR-N) and granite (GA), yielded δ26Mg mean values of −0.50 ± 0.08‰ and −0.75 ± 0.14‰, respectively. The weathering products, soil (TILL-1) and river water (NIST SRM 1640), gave δ26Mg values of −0.40 ± 0.07‰ and −1.27 ± 0.14‰, respectively. We also present, for the first time, the Mg isotope composition of bulk plant and organic matter. Rye flour (BCR-381), sea lettuce (Ulva lactuva) (BCR-279), natural hairgrass (Deschampsia flexuosa) and lichen (BCR-482) reference materials gave δ26Mg values of −1.10 ± 0.14‰, −0.90 ± 0.19‰, −0.50 ± 0.22‰ and −1.15 ± 0.27‰ respectively. Plant δ26Mg values fell within the range defined by published data for chlorophylls.

International audience; Forest ecosystems are often found on acid soils where calcium availability depends on two main inputs (atmospheric deposition and the weathering of soil minerals) and on the biological cycling of nutrients. In the context of global change (decreasing atmospheric inputs, increasing biomass exportation, climate change), it is important to determine calcium sources to the ecosystem and tree nutrition to better understand how forest ecosystems will respond to these changes over time. The aim of this study was to study and compare Ca pools and cycling in two mature forest ecosystems (Clermont en Argonne and Azerailles) developed on two contrasting polycyclic soils (Lorraine plateau, eastern France) and identify the Ca sources contributing to ecosystem functioning. At both sites, soil Ca pools were measured; atmospheric deposition of Ca was monitored from bulk precipitation and throughfall chemistry; Ca biological cycling was assessed by measuring litterfall and by a litter decomposition experiment; strontium (87Sr/86Sr) isotope data in the soil profile (fine roots, exchangeable pool, bulk soil) was used to estimate the distribution of Sr and Ca uptake in the soil profile and the relative contribution of mineral weathering in the soil layers to total ecosystems inputs. Despite important differences in Ca availability in the topsoil between both sites, tree growth and nutrition indicators showed no significant difference. This discrepancy is not explained by the biological cycling of Ca but may be partly explained by higher Ca deposition at the Ca-poorer site. Strontium isotope data enabled to show important differences of Ca sources for tree uptake. At the Ca-poorer site, deep soil layers (> 105 cm) potentially represent from 32% to 100% of total Sr uptake. At the Ca-richer site, results suggest that uptake is more evenly distributed in the soil profile. Sr isotope data coupled with a modeling approach suggest that two different mineral sources exist in the soil profile: a radiogenic Sr source in the topsoil (87Sr/86Sr > 0.717) and a less radiogenic source in depth (87Sr/86Sr < 0.717). The deep mineral source may represent from 40% to 86% of total Sr inputs at the poorer site and from 25% to 86% at the richer site. The origin of this deep strontium source is unclear but soil mineralogy suggests an allochthonous origin. We hypothesize that this deep source originates from capillary rise of the groundwater aquifer. This nutrient input to forest ecosystems is not commonly taken into account but may strongly participate in maintaining the chemical fertility of soils over time.

cited By 0; International audience; Chloride is often considered as the main chlorine form in soils. However, recent studies show that chlorine is mostly present in soils as naturally produced organically bound molecules. The relative contribution of biotic, including microbial, and abiotic processes to formation of organically bound chlorine remains poorly understood. We performed a37Cl spiking batch experiment with a forest soil incubated under abiotic and biotic conditions over two time periods to simultaneously monitor the formation of organically bound chlorine from natural and tracer chlorine. To compare biotic and abiotic conditions without biased effect of sterilization technique for abiotic control, the soil was irradiated and reinoculated or not with soil microflora. Fifteen days after microbial inoculation, the natural non-extractable organic chlorine content in the inoculated soil was significantly higher than in the sterile soil, showing that microbial activity contributed to formation of organically bound chlorine. However, no significant difference was noted between the two incubation periods. The same trend was noted for tracer chlorine, yet without a significant difference. The present study shows that chlorination is mediated by microbial activity, but there is also some indication of abiotic formation of organically bound chlorine, with a non-extractable organic tracer chlorine formation of about 6% just after spiking in abiotic conditions. © 2016 Elsevier Ltd

The mean depth of Sr and water uptake in mixed Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) stands was investigated, using natural variations of 87Sr/86Sr and 18O/16O in soils in relation to depth. Three spruce-pine pairs were studied on a podzol and a peat site in Northern Sweden. Tree leaf and wood, as well as soils, soil solutions and roots below each tree were analysed for Sr and Ca concentrations and 87Sr/86Sr ratio. The 18O/16O ratio was also determined in xylem sap and soil solutions in relation to depth. Soil solution 18O/16O decreased in relation to depth. Comparing with xylem sap 18O/16O data indicated a deeper uptake of soil water by pine than spruce on the podzol site and a superficial uptake by both species on the peat. The 87Sr/86Sr ratio of bioavailable Sr generally increased in soils in relation to depth. Contrastingly, the 87Sr/86Sr ratio in spruce wood was generally higher than in pine wood suggesting a deeper uptake of Sr by spruce. But the 87Sr/86Sr ratio and concentrations of bioavailable Sr were systematically higher below spruce than below pine. In order to explain these unexpected results, we built a simple flux model to investigate the possible effects of interspecific variations in Sr cycling, soil mineral weathering and depth of Sr uptake on soil and tree 87Sr/86Sr ratio. At the study sites, spruce cycled in litterfall up to 12 times more strontium than pine. The use of the model showed that this difference in Sr cycling could alone explain higher isotopic signatures of trees and topsoils below spruce. Besides, high isotopic signatures of roots in the A/E horizons below spruce led us to hypothesise a species-specific weathering process. Finally, the comparison between the 87Sr/86Sr ratios in wood and root or soil solutions below each species suggested that the average depth of Sr and water uptake were close, but irregular variations of the Sr isotopic ratio with depth reduce the accuracy of the results. Tree species strongly influence Sr isotopic ratios in boreal forest soils through differences in Sr cycling, and possibly through specific mineral weathering.

The objective of this study was to assess the time variation of mineral and water stress levels across the life of a declining, Mg-deficient, spruce stand, in order to clarify the factors that caused the decline. Since 1985, strong soil acidification linked to a large leaching of nitrate and base cations was measured at the study site. In 1994, 5 trees were felled and tree rings were measured and analysed for Ca, Mg, K, Sr, 13C12C and 87Sr/86Sr isotopic ratios. Strontium pools and fluxes as well as root Sr isotope ratio in relation to depth were also measured. Wood chemical concentrations and isotope ratios were strongly related to the dominance status of each tree. On average during the study period, the 87Sr/86Sr ratio of spruce wood decreased. Using a mechanistic model computing long term variations of 87Sr/86Sr ratio in trees and soils, we reproduced the observed trend by simulating soil acidification – increasing Sr drainage from the whole profile, and particularly from the organic horizon –, and root uptake becoming more superficial with time. Between 1952 and 1976, tree ring Δ 13C decreased strongly and continuously, which, in addition to other factors, might be related to an increase in water stress. Thus, a decrease in rooting depth, possibly related to soil acidification, appeared as a possible cause for the long term increase in water stress. The extreme drought event of 1976 appears to have revealed and triggered the decline.

The contribution of deep tree roots to the nutrition of a tropicalrainforest were studied along an edaphic transect in French Guyana. Soil typeswere mapped in relation to the texture of the upper horizons and the depth ofoccurrence of the loamy saprolite. The position of mature individuals of fourcommon species, differing by they rooting depth, was identified and tree leaveswere analysed for major nutrients and strontium (Sr) isotopic ratios.On average, the range of leaf isotopic ratio (87Sr/86Sr= 0.714–0.716) was narrow compared to that of bulk soils(87Sr/86Sr = 0.72–0.77). Steep gradients ofincreasing 87Sr/86Sr in roots with soil depth were foundin all investigated profiles, which indicated that the flux of Sr deposited inrain and leached from the litter layer was tightly retained in the upper soillayers. Over the whole of the site, as well as within each soil unit, tree87Sr/86Sr ratios were very similar whatever the species,and close to litter and near-surface roots 87Sr/86Srratios, suggesting no or very little Sr contribution from deep tree roots.Variations of Ca and Sr concentrations in leaves were strongly correlated butnot with leaf 87Sr/86Sr ratios. These results support thetheory that Sr and Ca uptake and cycling are mostly superficial in tropicalrainforests.

In favourable conditions, the 87Sr/86Sr isotope ratios of the Sr delivered by rain and soil mineral weathering differ. Assuming that Ca and Sr behave similarly in forest ecosystems, several authors have used the 87Sr/86Sr variation in forest compartments to calculate the contribution of rain and mineral weathering to Ca fluxes and pools. However, there are a number of experimental reports showing that Ca and Sr may behave differently in the soil and in the plant. We have tested this Ca–Sr analogy in the field by measuring the variation of Sr and Ca concentrations, fluxes and pools in spruce, beech and maple stands on granite, sandstone and limestone. Results show that (1) variations of Ca and Sr concentrations are generally correlated at each level of the ecosystems. (2) In spruce on acid soils, a preferential uptake of Ca over Sr occurs (Aubure spruce Sr/Ca = 0.8×10−3; soil exchangeable Sr/Ca between 2 and 6×10−3). On calcareous soils, a preferential uptake of Sr over Ca by spruce may occur. (3) In spruce and beech on acid and calcareous soils, a preferential translocation of Ca over Sr from roots to leaves occurs ((Sr/Ca) in leaves was between 10 and 90% of that in roots). (4) The biological cycling of Ca and Sr leads to an enrichment of the upper soil layers in Ca and Sr. Compared to Sr, Ca accumulates in the upper layer of acid soils because Ca cycling through litterfall is favoured over Sr cycling, and possibly because of the selectivity of acid organic exchangers for Ca.

To demonstrate directly soil acidification under spruce stands in the Strengbach catchment, soils from two adjacent stands aged 40 and 90 years were sampled intensively in 1990 and resampled in 1996. Soils already were very acid in 1990. Between 1990 and 1996, soils had experienced a significant decrease in exchangeable Ca2+ and Mg2+ at all depths at the two sites except in the 0–10 cm layer, for which base saturation remained constant. Losses of Ca2+ calculated from a budget study at the same sites and from the comparison of exchangeable stores were similar. In contrast, the loss of Mg2+ from the exchange complex was higher than that computed from the field budget. Various reasons, including most probably uncertainties linked to the extremely low levels of Mg in the ecosystem, may explain this discrepancy. Since 1987, a general decrease of the (Ca2+ Mg2+)/Al3+ ratio in soil solution was observed at both sites. These results are consistent with present day acidification of soils poor in weatherable minerals under spruce stands in the Vosges Mountains.

Forest soil fertility is generally estimated by studying the water and nutrient cycles essential to living organisms (i.e. biogeochemical cycles). Use of geochemical and/or isotopic tracers is an innovative, complementary approach to more traditional studies. Experimental procedures and results of some recent studies in forest ecosystems using natural tracers (e.g. 18O, 13C, 26Mg) or artificially supplied tracers (e.g. enrichment in Sr, Rb, 15N, 44Ca, 26Mg, 32P) are presented. Results are discussed in terms of relevance for using these tools to identify sources, to estimate residence times of water and elements, and to trace nutrient fluxes, of both organic and mineral origins, that are internal or external to the ecosystem.; La fertilité des sols forestiers est généralement estimée par l'étude des cycles de l'eau et des éléments nutritifs essentiels aux êtres vivants (cycles biogéochimiques). Parmi l'ensemble des méthodes d'étude de ces cycles, une approche innovante, complémentaire des études plus classiques, consiste à utiliser des traceurs géochimiques ou isotopiques. Les démarches expérimentales et résultats de quelques études récentes dans le domaine, utilisant des traceurs naturellement présents dans les écosystèmes (ex. 18O, 13C, 26Mg) ou artificiellement apportés (ex. enrichissements en Sr, Rb, 15N, 44Ca, 26Mg, 32P) seront présentés. Ces résultats seront discutés pour faire un point sur la pertinence d'utilisation de ces outils pour définir les sources, avoir accès au temps de résidence de l'eau et des éléments, et tracer les flux de nutriments qu'ils soient d'origine organique ou minérale, internes ou externes à l'écosystème.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN [Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; Forest soil fertility is generally estimated by studying the water and nutrient cycles essential to living organisms (i.e. biogeochemical cycles). Use of geochemical and/or isotopic tracers is an innovative, complementary approach to more traditional studies. Experimental procedures and results of some recent studies in forest ecosystems using natural tracers (e.g. 18O, 13C, 26Mg) or artificially supplied tracers (e.g. enrichment in Sr, Rb, 15N, 44Ca, 26Mg, 32P) are presented. Results are discussed in terms of relevance for using these tools to identify sources, to estimate residence times of water and elements, and to trace nutrient fluxes, of both organic and mineral origins, that are internal or external to the ecosystem.; La fertilité des sols forestiers est généralement estimée par l'étude des cycles de l'eau et des éléments nutritifs essentiels aux êtres vivants (cycles biogéochimiques). Parmi l'ensemble des méthodes d'étude de ces cycles, une approche innovante, complémentaire des études plus classiques, consiste à utiliser des traceurs géochimiques ou isotopiques. Les démarches expérimentales et résultats de quelques études récentes dans le domaine, utilisant des traceurs naturellement présents dans les écosystèmes (ex. 18O, 13C, 26Mg) ou artificiellement apportés (ex. enrichissements en Sr, Rb, 15N, 44Ca, 26Mg, 32P) seront présentés. Ces résultats seront discutés pour faire un point sur la pertinence d'utilisation de ces outils pour définir les sources, avoir accès au temps de résidence de l'eau et des éléments, et tracer les flux de nutriments qu'ils soient d'origine organique ou minérale, internes ou externes à l'écosystème.

The silicate mineral weathering potential of different weathering pattern soil bacteria was characterized, and links between key habitat determinants and soil bacteria strategies were established in this work. Phlogopite weathering experiments were conducted under aerobic conditions and in closed systems with bacterial communities isolated from different soil profiles that are typical of a temperate climate. Our results suggest that the phlogopite weathering processes (i.e., acidolysis and complexolysis processes) of bacterial communities is determined by soil horizons as a function of (i) organic matter content, (ii) impoverishment in clays in leached horizons and (iii) the content of exchangeable cations. In our experiments, bacterial communities developed two strategies for iron release from phlogopite: the first was the K-strategy, which is used by bacterial communities extracted from soil rich in nutrient elements (especially in horizons with high contents of exchangeable Mg, Ca, etc.) and organic carbon. These communities produced strong chelating organic acids in low concentrations and used small amounts of carbon. The other was the r-strategy for bacterial communities extracted from soils poor in nutrient elements and organic carbon content. They produced weak chelating organic acids in large amounts and used a large proportion of the carbon source.

Liming of forest ecosystem is recognized to increase nutrients availability in soil and water and to enhance the biomass and bacterial activities in soil. However, little studies have investigated on change induced on bacterial ability to alter silicate mineral after soil liming. Thus, this study is carried out in experimental conditions using podzol collected in the winter (2007), spring and summer (2008) in small forest catchments in Vosges Mountains amended in 2003 by dolostone and limestone. Bacterial communities, extracted from various horizons of these soils amended or not, were put in contact with a phyllosilicate (phlogopite as sole source of Mg and Fe) in miniaturized bioassays in aerobic conditions. A weathering phenotype was determined through the quantification of (i) protons and organic acids released in assay solution by bacteria (ii) iron leached from phlogopite lattice into solution by bacteria and (iii) the carbon source consumption (i.e. glucose). These results were then compared to empirical model based on chemical leaching experiments realized in the same conditions in order to simulate the processes involved. In parallel, the carbon source utilization patterns of bacteria were investigated in order to discriminate the bacterial communities from amended and non-amended soil horizons. The results indicate that (1) the total bacterial biomass was unaffected by the Ca–Mg amendment, whereas the cultivable bacterial biomass increased after the amendment, and (2) the weathering and the carbon source utilization patterns of bacterial communities differs from one soil horizon to another and among soil types. The metabolic profiles analyzed indicated significant differences in organic C substrate usage depending on season and Ca–Mg amendment. Bacterial communities, extracted from the amended soil, are enable greater iron leaching compared to those found in the control soil, suggesting a greater release of organic acids and/or a more highly chelating organic acid release. The process developed by bacteria to alter the phillosilicate is complexolysis. We conclude that the Ca–Mg amendment had a positive effect on the functional richness of bacterial communities extracted from soil and on their potential to weather minerals that was present after several years.

Equipe Agrohydrologie; International audience; The intensification of agriculture in recent decades has resulted in extremely high nitrogen inputs to ecosystems. One effect has been H+ release through NH4+ oxidation in soils, which increases rock weathering and leads to acidification processes such as base-cation leaching from the soil exchange complex. This study investigated the evolution of cation concentrations over the past 50 years in rivers from the Armorican crystalline shield (Brittany, western France). On a regional scale, acidification has resulted in increased base-cation riverine exports (Ca2+, Mg2+, Na+, K+) correlated with the increased NO3- concentration. The estimated cation increase is 0.7 mmol(+)/L for Ca2+ + Mg2+ and 0.85 mmol(+)/L for total cations. According to mass balance, cation loss represents >30% of the base-cation exchange capacity of soils. Long-term acidification thus contributes to a decline in soil productivity. Estimates of the total organic nitrogen annually produced worldwide indicate that acidification may also constitute an additional carbon source in crystalline catchments if compensated by liming practices.

Weathering experiments using biotite and phlogopite in the presence of bacteria were conducted to better understand biotic dissolution kinetics and processes (proton- and ligand-promoted dissolution) under aerobic conditions. Miniature batch reactors (300 μl in microplate wells) were used at 24 °C for 3 days with and without bacterial strains. Abiotic experiments were performed with organic and nitric acids in order to calibrate the biotite–phlogopite chemical dissolution. An empirical model was used to fit the pH dependence for iron release rate (rFe) considering the influence of both protons and ligands from acidic to neutral conditions (pH ranging from 3 to 7): r Fe = k H ( a H + ) m + k L ( a L ) 1 where k is the apparent rate constant, aH+ and aL are the activities of protons and ligands, and m and l are the reaction orders. For both minerals in most cases at a given pH, the iron release rates in the presence of bacteria were in good agreement with rates determined by the chemical model and could be explained by a combination of proton- and ligand-promoted processes. Bacteria affect mineral dissolution and iron release rates through the quantities and nature of the organic acids they produce. Three domains were differentiated and proposed as biochemical models of mica dissolution: (1) below pH 3, only proton-promoted dissolution occurred, (2) in weakly acidic solutions both ligand- and proton-promoted mechanisms were involved, and (3) iron immobilization occured, at pH values greater than 4 for biotite and greater than 5 for phlogopite. This model allows us to distinguish the “weathering pattern phenotypes” of strains. Bacteria that are isolated from horizons poor in carbon appear more efficient at weathering micas than bacterial strains isolated from environments rich in carbon. Moreover, our results suggest that the mineral could exert a control on the release of organic acids and the “weathering pattern phenotypes” of bacteria.

Two higher plant species (rye grass and clover) were cultivated under laboratory conditions on two substrates (solution, phlogopite) in order to constrain the corresponding Mg isotope fractionations during plant growth and Mg uptake. We show that bulk plants are systematically enriched in heavy isotopes relative to their nutrient source. The Δ26Mgplant-source range from 0.72‰ to 0.26‰ for rye grass and from 1.05‰ to 0.41‰ for clover. Plants grown on phlogopite display Mg isotope signatures (relative to the Mg source) ∼0.3‰ lower than hydroponic plants. For a given substrate, rye grass display lower δ26Mg (by ∼0.3‰) relative to clover. Magnesium desorbed from rye grass roots display a δ26Mg greater than the nutrient solution. Adsorption experiments on dead and living rye grass roots also indicate a significant enrichment in heavy isotopes of the Mg adsorbed on the root surface. Our results indicate that the key processes responsible for heavy isotope enrichment in plants are located at the root level. Both species also exhibit an enrichment in light isotopes from roots to shoots (Δ26Mgleaf-root = −0.65‰ and −0.34‰ for rye grass and clover grown on phlogopite respectively, and Δ26Mgleaf-root of −0.06‰ and −0.22‰ for the same species grown hydroponically). This heavy isotope depletion in leaves can be explained by biological processes that affect leaves and roots differently: (1) organo–Mg complex (including chlorophyll) formation, and (2) Mg transport within plant. For both species, a positive correlation between δ26Mg and K/Mg was observed among the various organs. This correlation is consistent with the link between K and Mg internal cycles, as well as with formation of organo–magnesium compounds associated with enrichment in heavy isotopes. Considering our results together with the published range for δ26Mg of natural plants and rivers, we estimate that a significant change in continental vegetation would induce a change of the mean river δ26Mg that is comparable to analytical uncertainties.

From the summit downslope a granitic inselberg in French Guiana, soils and vegetation evolve from bare granite covered by cyanobacteria, to a savannah-type vegetation on thin patchy sandy accumulations, then to a low forest on shallow young soils and to a high forest on deep highly weathered ultisols. We have used element budgets and Sr isotopic variations in soils and plants to investigate the mineral nutrient supply sources of the different plant communities. Granite and atmospheric deposition have 87Sr/86Sr ratios of 1.3 and 0.71, respectively. The 87Sr/86Sr ratio of cyanobacteria (0.72) suggests granite weathering by cyanobacteria crusts. The 87Sr/86Sr ratio of the savannah-type vegetation is 0.73 and varies between 0.75 and 0.76 in the low and high forest leaf litter regardless of soil depth, age and degree of impoverishment. These almost constant ratio suggest that forest Sr comes from rainwater and from the summit of this inselberg, where it is released and redistributed along the slope, by surface flow, lateral redistribution of litter, and mineral particles. However, because of its very low content in the rock and soils, Ca is supplied to plants by atmospheric deposition., Du sommet vers la base d’un inselberg granitique (Nouragues, Guyane Française), les sols et la végétation évoluent depuis des savanes sur des ilots sableux entre les affleurements rocheux couverts de cyanobactéries, vers une forêt basse sur sols peu épais, riches en minéraux altérables puis une forêt haute sur sols très profonds et altérés. Les variations isotopiques du strontium des sols et des plantes ont été mesurées pour rechercher les sources de nutriments des différentes communautés végétales. Les rapports 87Sr/86Sr du granite et des dépôts atmosphériques sont respectivement de 1,3 et 0,71. Le rapport 87Sr/86Sr des cyanobacteries (0,72) suggère une libération de Sr par altération du granite. Le rapport 87Sr/86Sr de la savanne est de 0,73 et varie entre 0,75 et 0,76 dans les litières de forêt basse et haute, quelle que soit la profondeur, et la richesse en minéraux altérables des sols. La faiblesse et l’homogénéité surprenante de ces rapports suggèrent une alimentation en Sr des forêts essentiellement à partir de dépôts atmosphériques et des sols de la partie haute de l’inselberg, via des écoulements de surface, des redistributions latérales de litière et de particules minerales lors de crises érosives. Cependant, en raison de l’extrême pauvreté de la roche et des sols en calcium, le Ca des communautés végétales provient de la pluie.

To demonstrate directly soil acidification under spruce stands in the Strengbach catchment, soils from two adjacent stands aged 40 and 90 years were sampled intensively in 1990 and resampled in 1996. Soils already were very acid in 1990. Between 1990 and 1996, soils had experienced a significant decrease in exchangeable Ca2+ and Mg2+ at all depths at the two sites except in the 0-10 cm layer, for which base saturation remained constant. Losses of Ca2+ calculated from a budget study at the same sites and from the comparison of exchangeable stores were similar. In contrast, the loss of Mg2+ from the exchange complex was higher than that computed from the field budget. Various reasons, including most probably uncertainties linked to the extremely low levels of Mg in the ecosystem, may explain this discrepancy. Since 1987, a general decrease of the (Ca2++ Mg2+)/Al3 ratio in soil solution was observed at both sites. These results are consistent with present day acidification of soils poor in weatherable minerals under spruce stands in the Vosges Mountains.

International audience; This study presents a chemical protocol for the separation of Mg that is particularly adapted to alkali-rich samples (granite, soil, plants). This protocol was based on a combination of two pre-existing methods: transition metals were first removed from the sample using an AG-MP1 anion-exchange resin, followed by the separation of alkalis (Na, K) and bivalent cations (Ca 2+ , Mn 2+ and Sr 2+) using a AG50W-X12 cation-exchange resin. This procedure allowed Mg recovery of ~100 ± 8%. The [Σcations]/[Mg] molar ratios in all of the final Mg fractions were lower than 0.05. The Mg isotope ratios of eleven reference materials were analysed using two different MC-ICP-MS instruments (Isoprobe and Nu Plasma). The long-term reproducibility, assessed by repeated measurements of Mg standard solutions and natural reference materials, was 0.14‰. The basalt (BE-N), limestone (Cal-S) and seawater (BCR-403) reference materials analysed in this study yielded δ 26 Mg mean values of-0.28 ± 0.08‰,-4.37 ± 0.11‰ and-0.89 ± 0.10‰ respectively, in agreement with published data. The two continental rocks analysed, diorite (DR-N) and granite (GA), yielded δ 26 Mg mean values of-0.50 ± 0.08‰ and-0.75 ± 0.14‰, respectively. The weathering products, soil (TILL-1) and river water (NIST SRM 1640), gave δ 26 Mg values of-0.40 ± 0.07‰ and-1.27 ± 0.14‰, respectively. We also present, for the first time, the Mg isotope composition of bulk plant and organic matter. Rye flour (BCR-381), sea lettuce (Ulva lactuva) (BCR-279), natural hairgrass (Deschampsia flexuosa) and lichen (BCR-482) reference materials gave δ 26 Mg values of-1.10 ± 0.14‰,-0.90 ± 0.19‰,-0.50 ± 0.22‰ and-1.15 ± 0.27‰ respectively. Plant δ 26 Mg values fell within the range defined by published data for chlorophylls.

As part of an approach focusing on the phases of anthropisation of the Vosges mountains, which has already begun on the Alsatian slope and the Haut-Vosges, this project, which combines archaeo-geography and geoarchaeology, aims to measure, over the long time, the dynamics of a medium-altitude forest area, located on the Lorraine slope, a priori impacted by Man. The choice of the Fossard Massif as the object of study, which extends over a hundred km² to the north of Remiremont (Vosges), is the result of its close topographical and historical link with this town, born of an abbey originally founded, in the 7th century, in a late-antique castrum, situated at an altitude of 670 m at the southern end of this relief and today known as "Le Saint-Mont" (Saint-Amé, Vosges).; Dans le cadre d’une démarche portant sur les phases d’anthropisation de la montagne vosgienne, déjà commencée sur le versant alsacien et les hautes-Vosges, ce projet, mêlant archéogéographie et géoarchéologie, vise à mesurer, sur la longue durée, la dynamique d’un espace forestier de moyenne altitude, situé sur le versant lorrain, a priori impacter par l’Homme. Le choix, comme objet d’étude, du massif du Fossard, qui s’étend sur une centaine de km² au nord de Remiremont (Vosges), résulte de son lien étroit, topographique et historique, avec cette ville née d’une abbaye primitivement fondée, au VIIe siècle, dans un castrum tardo-antique, perché, à 670 m d’altitude à l’extrémité méridionale de ce relief et aujourd’hui dénommé «Le Saint-Mont » (Saint-Amé, Vosges).

In the Early Modern Age (16th - 18th centuries), the construction of ocean-going ships was paramount to the development of cultural encounters in what became the Age of Discovery and European expansion. Spain was one of the biggest forces of that time. The European project “ForSEAdiscovery” seeks answers in this context to the following key questions: Could Spanish forest resources sustain the increasing demand of timber, or were the wood imported from elsewhere? If Spanish forests were not the only wood supplier, how were the trade networks organized? This project will address these questions through a multidisciplinary and innovative training research program to improve the understanding of our historical past, our cultural heritage, and our knowledge of the use of resources for shipbuilding. The objective of this PhD thesis, taking part of this project, is to identify the provenance of the Iberian shipbuilding wood using geochemical tracers. The hypothesis is that trees growing on contrasted rocks and soils have specific geochemical signatures, which can be an indicator of geographic provenance. In this context, the Sr isotopic signature (87Sr/86Sr) was characterized in shipwreck wood samples and wood from living trees, soils and rocks collected from the Spanish forest stands indicated as potential source of wood between the 16th - 18th centuries. The δ88/86Sr signatures were also characterized in the samples. The rock types and ages were characterized at the selected sites and the link between the 87Sr/86Sr and δ88/86Sr in rocks, soils and trees was studied on the sampled Spanish sites. The local signature of Spanish potential sites was determined for provenance of wood. Our results indicate that 87Sr/86Sr isotope ratios in trees reflect the signature of the corresponding soil exchangeable pool while δ88/86Sr was shown to be affected by mass-dependent fractionation with trees taking up lighter (86Sr) isotopes, leaving the soil exchangeable pool enriched with the heavier isotopes (88Sr). This fractionation observed for oak trees, was not found in pines suggesting that the isotopic fractionation during tree uptake is species dependent. The contamination of wood from shipwrecks by seawater elements was identified. Marine Sr was found to be adsorbed on the wood or included in the precipitated minerals in the waterlogged wood. Several extraction experiments were tested and an adapted protocol was developed to extract the seawater elements and retrieve the original signature of the archaeological wood. We succeeded to validate an extraction protocol and retrieve the original signature of one wood sample. This result underline the potential and importance of a new method combining 87Sr/86Sr and δ88/86Sr values for future provenance studies on wood or other materials. However, our results also indicated that most of our shipwreck wood samples did not conserve their original Sr. Therefore, preconizations were suggested in order to extend the use of this tracer in future provenance studies on archaeological wood from shipwrecks, Au début des temps modernes (16ème - 18ème siècles), la construction de grands navires était primordiale pour le développement des rencontres culturelles dans ce qui est devenu l'âge de la découverte et de l'expansion européenne. L’Espagne était une des grandes puissances de l’époque. Le projet européen « ForSEAdiscovery » cherche dans ce contexte à répondre aux questions clés suivantes : les ressources forestières ibériques de l’époque soutenaient-elles la demande croissante de bois, ou bien ce bois était-il importé d’autres pays ? Si ces bois ne provenaient pas de l’Espagne, comment les réseaux de commerce étaient-ils organisés ? Ce projet aborde ces questions à travers un programme de recherche multidisciplinaire et innovant pour améliorer la compréhension de notre passé historique et de notre patrimoine culturel, et développer notre connaissance sur l'utilisation passée des ressources en bois pour la construction navale. L'objectif de cette thèse, qui s’insère dans ce projet, est d’identifier la provenance des bois utilisés dans la construction navale ibérique en utilisant des traceurs géochimiques. L’hypothèse est que les arbres se développant sur des roches et des sols contrastés possèdent des signatures géochimiques spécifiques héritées des roches. Les signatures isotopiques en strontium (87Sr/86Sr) peuvent notamment être des indicateurs de provenance géographique. Dans ce contexte, la démarche suivie dans la thèse a consisté à caractériser la signature isotopique en Sr dans des bois d'épaves de bateaux et dans les bois d’arbres actuels, les sols et roches prélevés dans les principaux peuplements forestiers espagnols pointés comme lieux de production des bois entre le 16ème - 18ème siècles. Les signatures en δ88/86Sr, traceur peu connu encore, ont également été caractérisées dans les échantillons. Les types et les âges des roches ont été caractérisés et les liens entre les rapports isotopiques 87Sr/86Sr et δ88/86Sr dans les roches, sols et arbres ont été étudiés sur les sites espagnols échantillonnés. La signature locale des sites espagnols potentiels de provenance de bois a été déterminée. Nos résultats mettent en évidence que le rapport isotopique 87Sr/86Sr dans les arbres reflète la signature de la fraction échangeable des sols sur lesquels ils croissent alors que le δ88/86Sr est affecté par le fractionnement, les isotopes légers (86Sr) étant préférentiellement incorporés dans les arbres laissant la fraction échangeable du sol enrichie avec les isotopes lourds (88Sr). Ce fractionnement observé pour les chênes, n’est pas marqué dans le bois des pins suggérant que le fractionnement isotopique durant le transfert du Sr entre le sol et l’arbre est dépendant de l’espèce. La contamination des bois d’épaves par les éléments marins a été identifiée. Le Sr marin se retrouve notamment sous forme adsorbée ou dans la structure des minéraux précipités dans les bois immergés. Différentes expériences d’extractions ont été testées et un protocole adapté a été développé pour extraire les éléments marins et retrouver la signature originelle du bois archéologique. Nous avons réussi à valider un protocole d’extraction et retrouver la signature originelle d’un échantillon de bois d’épave. Ce résultat souligne le potentiel et l’importance d’une nouvelle méthode combinant 87Sr/86Sr et δ88/86Sr pour des futures études de provenance de bois ou autres matériaux. Cependant, nos résultats indiquent également que beaucoup de nos échantillons de bois archéologiques n’ont pas conservé leur Sr originel. Partant de ce constat, des préconisations sont proposées pour améliorer la possibilité d’utilisation de ce traceur dans les études futures de provenance de bois archéologiques sous-marins

Recent studies have shown that organic chlorine is retained in the soil and is formed by a chlorination process mainly from the microbial activity of the soi still poorly documented. The aim of this study is to estimate the organic and inorganic forms of chlorine in contrasting soil and highlight the evolution of these forms according to certain environmental parameters or terms of incubations and to the activity of microorganisms. For this, the organo-mineral horizons of contrasting soil were studied (i) in situ: The amounts of chlorine and physico-chemical and microbiological parameters of soil were measured; (ii) in two experimental devices incubations under different conditions. Measurements of chlorine levels between the beginning and the end of the first experiment were measured by AOX analyzer. For the second experiment, the soil was previously enriched with Na37Cl and 37Cl levels were measured by HR ICP MS. Soil samples from these incubations were analyzed by Xanes spectrometry to identify the speciation of chlorine forms in soils. Soil non-extractable organic chlorine contents represent almost all of the chlorine. The parameters that influence the distribution of chlorine contents in soils correspond to vegetation cover, pH, organic carbon content and quantities of microorganisms. The chlorine contents measured by AOX analyzer and by HR ICP MS highlight an organic chlorine formation over time in relation to the microorganims in the soil. The measures carried out by HR ICP MS show also an organic chlorine formation in abiotic conditions. Conversely, XANES spectrometry measurements have show any organic chlorine formation, Des études ont démontré que du chlore organique est retenu dans les sols et serait formé par un processus de chloruration issu de l’activité microbienne des sols. Le but de cette étude est d’estimer les formes organiques de chlore dans des sols contrastés et de mettre en évidence l’évolution de ces formes de chlore selon certains paramètres environnementaux ou modalités d’incubations en fonction de l’activité des microorganismes. Les horizons organo-minéraux de sols contrastés ont été étudiés (i) in situ : Les quantités de chlore et les paramètres physico-chimiques et microbiologiques de sols ont été mesuré ; (ii) dans deux dispositifs d’incubations sous différentes modalités. Les mesures des teneurs en chlore entre le début et la fin de la première expérience ont été mesurées par analyseur d’AOX. Pour la deuxième expérience, les sols ont été enrichis en Na37Cl et les teneurs en 37Cl ont été mesurées par ICP MS HR. Des mesures par spectrométrie Xanes ont été réalisées pour préciser la spéciation du chlore des sols. Les teneurs en chlore organique non extractibles représentent presque la totalité du chlore. Les paramètres qui influencent la répartition des teneurs en chlore correspondent au couvert végétal, au pH, à la teneur en carbone organique et aux quantités de microorganismes. Les teneurs en chlore mesurées par analyseur d’AOX et par ICP MS HR ont permis de mettre en évidence une formation de chlore organique en relation avec les paramètres microbiologiques. Les mesures par ICP MS HR ont montré une formation de chlore organique en conditions abiotiques. Les analyses par spectrométrie XANES n’ont pas permis de mettre en évidence une formation de chlore organique

Therefore, a problem appeared how to estimate the cost to engender by the damage of these floods on the various stakes (housing environment, industry, farming ?). A lot of economic evaluations were created, certain more reliable and more relevant. Among them, the Cost Benefits Analysis (CBA) which allows the project leaders to appreciate economically profits and costs of their projects. It allows to compare different various of the same project to define the most profitable from an economic point of view. It's within the framework of the elaboration of the action plan of prevention against the floods of the FENSCH, that the conurbation of the Val de Fensch in appointed EGIS Water to realize the CBA of this study. The realization of this file with necessity of the bibliographical researches on the different economic valuation methods existing, to understand and to synthesize the methodology to use for the CBA to apply it to the study of the FENSCH and obtain a result of profitability to be presented to the project leaders.; Aujourd'hui la ressource en eau est un enjeu prioritaire pour notre société. La lutte contre les inondations fait partie intégrante de cet objectif. Son développement est majeur depuis quelques années. De ce fait, une problématique est apparu, comment estimer les coûts engendrer par les dommages de ces inondations sur les différents enjeux (habitats, entreprises, agricultures ?). De nombreuses études d'évaluations économiques ont été créées, certaines plus fiable et plus pertinente. Parmi elles, l'Analyse Coûts Bénéfices (ACB) qui permet aux porteurs de projets d'apprécier économiquement les bénéfices et les coûts de leurs projets. Elle permet de comparer différentes variantes d'un même projet afin de définir la plus rentable d'un point de vue économique. C'est dans le cadre de l'élaboration du Programme d'Action et de Prévention des Inondations (PAPI) de la FENSCH, que la communauté d'Agglomération du Val de Fensch à mandaté EGIS EAU pour réaliser l'ACB de cette étude. La réalisation de ce dossier à nécessité des recherches bibliographiques sur les différentes méthodes d'évaluations économiques existantes, de comprendre et de synthétiser la méthodologie utiliser pour l'ACB afin de l'appliquer sur l'étude de la FENSCH et ainsi obtenir un résultat de rentabilité à présenter aux porteurs de projets.

The bacteria, through their diversity and activities play an important role in soil functioning. They are actively involved in the degradation of organic matter (OM) and this function is often used as an indicator of the biological quality of soils. The heterotrophic bacteria are also involved directly or not to the weathering of silicate minerals (group of primary and secondary minerals in soils). The silicate weathering controlled the leaching of essential major mineral elements (e.g. Fe, Mg) in solution, the neutralization of acids in soils (from atmospheric deposition, degradation of litter, biological activity) and the sequestration of atmospheric CO2. This step is therefore essential to maintaining soil fertility in terrestrial ecosystems. However, although the main weathering processes of silicates are well known in aerobic (i.e. the proton- and ligand-promoted dissolution), this function of bacterial weathering of silicate minerals has never been used as a biological indicator of soil fertility. In fact, there is no simple standardized method to identify these processes, especially when they can be accelerated or enhanced by more or less specific root and / or microbial activities. The first aim of this work was therefore to identify the process of weathering in two phyllosilicates (biotite, phlogopite) by heterotrophic bacteria and their variability. The originality of this work is to use an empirical model of silicates weathering based on the activity of protons and ligands to identify and study the interactions between bacteria and minerals. Tracing of weathering processes by isotopic approach using stable isotopes of magnesium has also been tested. The second aim of this work was to correlate the “silicate weathering” function of bacterial communities of various soils in field conditions. This study confirms that the partial oxidation of glucose to organic acids is the predominant mechanism by which bacteria accelerate the leaching of elements (Fe, Mg...) under aerobic conditions during the weathering of biotite and phlogopite especially at pH close to neutrality. The results demonstrate that bacteria secrete organic acids. The nature and quantity of these acids depend on the nature of limiting nutrients and more generally the experimental conditions of growth. The empirical model used has been adapted to compare the initial release rate of iron (and other elements) in bacterial and abiotic weathering of mica to identify the two major processes (i.e. the proton- and ligand-promoted dissolution) involved. This approach highlighted the identification of phenotypes according to the metabolism and the competence of the bacterial strains used. The study with stable isotopes of Mg as tracers of weathering showed no fractionation during the proton- and ligandpromoted dissolution. Two tendencies could however be highlighted and appear accentuated when the fraction of Mg leached increases: (1) where the dominant process is the the proton-promoted dissolution, Mg leach solution is enriched in heavy isotopes compared to the isotopic composition of phlogopite (2) when the dominant process is the ligand-promoted dissolution, Mg leach solution is enriched in light isotopes compared with phlogopite. Using the model in the second part of this work showed that the silicate weathering potential by microbial communities depends on their origin and in particular the contents of organic matter and nutrients (exchangeable cations) of soil horizons sampled. Two strategies of silicate weathering in these communities have been identified: (1) the bacterial communities isolated from organic and mineral nutrient-rich horizons released few organic acids, but very chelating. They have a slow metabolism (strategy = K) and very efficient, allowing a substantial release of iron, (2) communities isolated from organic and mineral nutrient-poor horizons release many low chelating organic acids. Their rapid metabolism (r = strategy) promotes the formation of new cells, but not an efficient release of iron. Finally, the interdisciplinary approach proposed in this work to identify and characterize the weathering of phyllosilicates by soil heterotrophic bacteria or communities in different environments. It provides a original and promising tool for identifying functional to evaluate the quality of natural soils or follow the restoration of anthropic soil., Les bactéries, via leur diversité et leurs activités, jouent un rôle important dans le fonctionnement des sols. Elles participent activement à la dégradation des matières organiques (MO) et cette fonction est souvent utilisée comme indicateur de la qualité biologique des sols. Les bactéries hétérotrophes participent aussi activement, directement ou indirectement, à l’altération des silicates, groupe prédominant de minéraux primaires et secondaires dans les sols. L’altération des silicates contrôle en partie la lixiviation d’éléments minéraux majeurs essentiels (Fe, Mg) en solution, la neutralisation d’acides dans les sols (issus des dépôts atmosphériques, de la dégradation des litières, de l’activité biologique), et la séquestration du CO2 atmosphérique. Cette étape clé est donc essentielle au maintien de la fertilité des sols dans les écosystèmes continentaux. Cependant, même si les principaux processus d’altération des silicates sont bien connus en milieu aérobie (i.e. l’acidolyse et la complexolyse), cette fonction d’altération bactérienne des silicates n’a jamais été utilisée comme indicateur biologique de la fertilité des sols. En fait il n’existe pas de méthode simple standardisée d’identification de ces processus surtout lorsque ceux-ci peuvent être accélérés ou amplifiés par des activités racinaires et/ou microbiennes plus ou moins spécifiques.Le premier objectif de ce travail de thèse a donc été d’identifier les processus d’altération de deux silicates modèles (biotite, phlogopite) par des bactéries hétérotrophes ainsi que leur variabilité. L’originalité de ce travail est d’utiliser un modèle d’altération empirique basé sur l’activité des protons et ligands pour identifier et étudier les interactions entre les bactéries et les minéraux. Le traçage des processus d’altération par une approche isotopique utilisant les isotopes stables du magnésium a également été testé. Le second objectif de la thèse a été de corréler la fonction d’altération de communautés bactériennes aux conditions naturelles rencontrées dans différents sols.Ce travail confirme que l’oxydation partielle du glucose en acides organiques est le mécanisme prédominant par lequel les bactéries amplifient la lixiviation d’éléments (Fe, Mg...) en condition aérobie lors de l’altération de la biotite et de la phlogopite, surtout pour des pH proches de la neutralité. Les résultats démontrent que les bactéries sécrètent des acides organiques dont la nature et la quantité sont fonction de la nature des nutriments limitants et plus généralement des conditions expérimentales de croissances. Le modèle empirique utilisé a été adapté pour permettre de comparer les taux de libération initiaux du fer (et d’autres éléments) lors de l’altération abiotique et bactérienne de micas afin d’identifier les deux processus majeurs (acidolyse et complexolyse) impliqués. Cette approche a permis de mettre en évidence des phénotypes d’altération en fonction du métabolisme et la compétence des souches bactériennes utilisées. L’étude menée avec les isotopes stables du Mg comme traceurs d’altération n’a pas montré de fractionnements signant chaque processus. Deux tendances ont pu cependant être mises en évidence et semblent accentuées lorsque la fraction de Mg lixivié augmente : (1) lorsquele processus dominant est l’acidolyse, le Mg lixivié en solution est enrichi en isotopes lourds par rapport à la composition isotopique de la phlogopite (2) lorsque le processus dominant est la complexolyse, le Mg lixivié en solution est enrichi en isotopes légers par rapport à la phlogopite. L’utilisation du modèle dans la seconde partie de ces travaux a permis de montrer que le potentiel d’altérationdes silicates par les communautés bactériennes dépend de leur origine et en particulier des teneurs en matière organique et en nutriments (cations échangeables) des horizons de sols échantillonnés. Deux stratégies d’altération des silicates par ces communautés ont pu être mises en évidence : (1) les communautés bactériennes isolées des horizons riches en MO libèrent peu d’acides organiques, mais très complexants. Elles ont un métabolisme lent (= stratégie K) et très efficace, permettant une libération importante de fer, (2) les communautés isolées d’horizons pauvres en MO libèrent beaucoup d’acides organiques avec un faible pouvoir complexant. Leur métabolisme rapide (= stratégie r) favorise la formation de nouvelles cellules, mais pas une libération efficace du fer.Pour conclure, l’approche interdisciplinaire proposée dans ce travail permet d’identifier et de caractériser les processus d’altération de phyllosilicates par des bactéries ou des communautés hétérotrophes du sol dans différents environnements. Elle offre un outil d’identification fonctionnel original et prometteur pour évaluer la qualité des sols naturels ou suivre la restauration des sols anthropisés.