title: Biotic and abiotic experimental identification of bacterial influence on calcium isotopic signatures.
abstract: In this study, we tested experimentally the influence of plant and bacterial activities on the calcium (Ca) isotope distribution between soil solutions and plant organs. Abiotic apatite weathering experiments were performed under two different pH conditions using mineral and organic acids. Biotic experiments were performed using either apatite or Ca-enriched biotite substrates in the presence of Scots pines, inoculated or not with the rhizosphere bacterial strain Bulkholderia glathei PML1(12), or the B. glathei PML1(12) alone. For each experiment, the percolate was collected every week and analyzed for Ca concentrations and Ca isotopic ratios. No Ca isotopic fractionation was observed for the different abiotic experimental settings. This indicates that no Ca isotopic fractionation occurs during apatite dissolution, whatever the nature of the acid (mineral or organic). The main result of the biotic experiments is the 0.22 ‰ (44)Ca enrichment recorded for a solution in contact with Scots pines grown on the bacteria-free apatite substrate. In contrast, the presence of bacteria did not cause Ca isotopic fractionation of the solution collected after 14 weeks of the experiments. These preliminary results suggest that bacteria influence the Ca isotopic signatures by dissolving Ca from apatite more efficiently. Therefore, Ca isotopes might be suitable for detecting bacteria-mediated processes in soils.
authors.affiliation: Laboratoire d'Hydrologie et de Géochimie de Strasbourg, Université de Strasbourg/EOST, CNRS, 1 rue Blessig, F-67000 Strasbourg, France.
authors.forename: Florian
authors.initials: F
authors.lastname: Cobert
authors.forename: Anne-Désirée
authors.initials: AD
authors.lastname: Schmitt
authors.forename: Christophe
authors.initials: C
authors.lastname: Calvaruso
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Turpault
authors.forename: Damien
authors.initials: D
authors.lastname: Lemarchand
authors.forename: Christelle
authors.initials: C
authors.lastname: Collignon
authors.forename: François
authors.initials: F
authors.lastname: Chabaux
authors.forename: Peter
authors.initials: P
authors.lastname: Stille
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry / Q000378:metabolism; D001031:Apatites / Q000737:chemistry / Q000378:metabolism; D019117:Burkholderia / Q000378:metabolism*; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002127:Calcium Isotopes / Q000032:analysis / Q000378:metabolism; D005296:Ferrous Compounds / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D041605:Pinus sylvestris / Q000378:metabolism* / Q000382:microbiology*; D018517:Plant Roots / Q000378:metabolism / Q000382:microbiology; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology
chemical_list: D000538:Aluminum Silicates; D001031:Apatites; D002127:Calcium Isotopes; D005296:Ferrous Compounds; D012987:Soil; C047410:biotite; D002118:Calcium