During her PhD studies, Nan Xu researched legumes, which are plants capable of fixing atmospheric dinitrogen into bioavailable nitrogen through symbiosis with nitrogen-fixing bacteria in their roots. Those plants are widely recognized as beneficial for carbon sequestration and increasing yields in forests and cropping systems. However, their effects on greenhouse gas emissions and nitrogen loss remain uncertain in the context of climate mitigation. Nan Xu discovered that the type of symbiotic bacteria was a critical factor influencing how nitrogen-fixing trees affects greenhouse gas emissions compared with non-nitrogen-fixing trees. In agricultural systems, legumes significantly increased soil N₂O emissions, nitrate leaching and plant nitrogen uptake relative to non-legumes.  In a field experiment, pea–barley intercropping consistently increased grain yield and grain nitrogen uptake compared with monocropping in the organic system with a history of manure fertilization. Her findings provide new insights for supporting climate-smart strategies for sustainable reforestation and agriculture.

The PhD study was completed at Agroecology Department, Faculty of Technical Sciences, Aarhus University.

This résumé was prepared by the PhD student.

Time: Tuesday, 2. June 2026 at 12:00
Place: Auditorium, Aarhus University,  Blichers Allé 20, 8830 Tjele
Title of PhD thesis: Impacts of nitrogen-fixing plants on soil greenhouse gas emissions and nitrogen losses: Insights from global reviews and a site-specific field experiment
Contact information: Nan Xu, e-mail: au725878@uni.au.dk, tel.: +45 91859818
Members of the assessment committee:
Professor Ana Meijide, Crop Science and Resource Conservation, University of Bonn, Germany
Associate Professor Dorte Bodin Dresbøll, Plant and Environmental Sciences, University of Copenhagen, Denmark
Professor Mogens Nicolaisen (chair), Agroecology, Aarhus University, Denmark
Main supervisor: Professor Diego Abalos, Agroecology, Aarhus University, Denmark
Co-supervisor: 
Tenure Track Assistant Professor Kirsten Lønne Enggrob, Agroecology, Aarhus University, Denmark
Professor Mathias Neumann Andersen, Agroecology, Aarhus University, Denmark
Language: The PhD dissertation will be defended in English

The defence is public.
The PhD thesis is available for reading at the Graduate School of Technical Sciences/GSTS, Ny Munkegade 120, building 1521, 8000 Aarhus C.