PhD Thesis Subject 2019-2022

Effect of the presence of bacteria on the isotopic fractionation of calcium in soils

This doctoral thesis topic proposes, using an experimental and theoretical study to lift different locks:

  • Identify the elementary isotopic fractionations of Ca in batch at the water-matrix-bacteria interface (fractionation intensity, influence of pH, initial Ca concentration, adsorption kinetics, matrix / solution ratio)
  • Identify the isotopic fractionation of Ca in a mesocosm (role of bacteria, roots, soil type)
  • Characterize the underlying fractionation mechanisms (Rayleigh / equilibrium, exchange / adsorption / desorption / complexation ...)

The project will test the potential of stable Ca isotopes, a methodology currently controlled by few laboratories, to specify the mechanisms for storage and release of nutrients in soils. The impact of the study will be both fundamental and applied research, including the development of a new indicator of nutrient bioavailability in soils.

It will be a question of setting up experiments (1) in batch to test the role of the micro-organisms on the isotopic fractionation of Ca, then (2) in mesocosms in order to identify the respective role of bacteria, minerals / humic compounds on isotopic fractionations.

This multi-disciplinary approach (geosciences, microbiology, chemistry) integrating the joint analysis of several isotopic systems will characterize the nutrient reservoirs and their interactions in the critical zone. Applying only one isotopic system to the understanding of natural mechanisms often only provides information on the processes and / or sources that affect it. The objective is thus to combine the "non-traditional" stable isotopes of Ca and Sr with two "stable conventional" isotopes such as C and N and a radiogenic isotope, the Sr. Indeed Ca, and Sr are natural competitors for the adsorption sites of organomineral particles, nitrogen can provide information on the state of bacterial nitrification (NH4 +, NO2-, NO3-), while C is a tracer conventionally used to trace organic processes in soils.

Required Skills:

Earth sciences, Isotopy, Soil sciences, chemistry, some notions of microbiology would be a plus

Host laboratory

The experimental work as well as the elementary and isotopic measurements will be carried out within the Laboratory of HYdrology and Geochemistry of Strasbourg (, and more particularly within the Isotope Biogeochemistry team and experimental (BIsE;

Please send me your resume, cover letter, copies of the transcripts of license, master 1 and first semester of master 2 and the name and contact information of two referees for Monday, May 13th to Anne-Desiree Schmitt A first selection will be made and a candidate will be proposed to apply to the doctoral school.

Do not hesitate to contact me if you want more information on the subject or the terms of the contest.

posted: 26 April 2019     Please mention EARTHWORKS when responding to this advertisement.