Applications are invited for a PhD fellowship at the Graduate School of Science and Technology, Aarhus
University, Denmark, within the Agroecology programme available from 1 May 2014 or later.
Title: Is dissolved organic nitrogen (DON) the key to plant-soil N cycling?
Research area and project description:
Efficient use of nutrients in agricultural systems is essential to meet a sustainable
intensification of the food production. Legumes add nitrogen (N) to soils via biological N2-fixation
which can substitute energy demanding mineral N fertilizers. Increasing the dependence on N from
legumes requires better knowledge of plant-soil N cycling to sustain crop production and reduce
environmentally harmful losses. A key issue is turnover of complex organic N forms to simpler organic N
forms, where the flow through the higher molecular weight (Mw) dissolved organic N (DON) pools have
been identified as the key process in the supply of N to plants from organic N sources. There is however at
lack of knowledge of the mechanisms controlling the fate of DON pools in soil.
The aim the project is to qualify and quantify the role of higher Mw DON in plant-soil N cycling in
cultivated ecosystems. In special focus is to elucidate the quantitative importance of plant organic N uptake,
the role of different organic N sources on the flow through the DON pools, and biotic and abiotic factors
affecting the availability of N for plant uptake. This is achieved by experimentation with double-labeling
(15N and 13C) of white clover followed by investigations of the fate and chemical nature of enriched DON in
plant-soil systems by among other compound-specific isotope analysis. The PhD-study within the project
will have a special focus the specific fate of DON fractions and the biotic drivers for DON cycling.
Specifically the PhD-fellow is to investigate:
(i) the flow through the DON pools in soil, and
(ii) microbial actors and activity in the treated soils.
Experimentally this is expected to include methods such as DON fractionation, compound-specific isotope
analysis, and investigations of biomarkers representing active microbial groups. Thus, the PhD-fellow will
be involved in experimental semi-field work, use of stable isotopes, and analytical chemistry to characterize
biomarkers and DON molecules.
Qualifications and specific competences:
Applicants to the PhD position must have a relevant Master’s degree (or graduate in the very near future –
documentation for final thesis and date of examination must be enclosed in the application) or equivalent.
The applicants shall preferably have a background in one or more of the following topic areas:
- analytical chemistry applied in biological systems,
- environmental chemistry, or
- agronomy/biology with a focus on plant-soil-microbial interactions.
Place of Employment and Place of Work:
The place of employment is Aarhus University (AU) and the place of work is the Department of Agroecology at
Research Centre Foulum, Blichers Allé 20, DK-8830 Tjele, Denmark.
Applicants seeking further information are invited to contact: Jim Rasmussen: firstname.lastname@example.org.
Please apply for the position before February 1st 2014 via: