Moisture effects on microbial protein biosynthesis from ammonium and nitrate in an unfertilised grassland

Michaela K. Reay*, Nadine Loick, Richard P. Evershed, Christoph Müller, Laura Cardenas

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review


Incorporation of nitrogen (N) into soil microbial protein is central to the soil N cycle to mitigate N losses and support plant N supply. However, the effect of factors, such as water filled pore space (WFPS), which influence inorganic N transformations and losses, and thus microbial incorporation, are only poorly understood. This work aimed to bridge this gap, using compound-specific 15N-stable isotope probing to quantify microbial assimilation into the largest defined soil organic N pool, protein-N. This approach applied differentially 15N-labelled ammonium nitrate (NH4NO3) to an unfertilised UK grassland in a soil mesocosm study over 10 days. The soil microbial community showed a strong preference for NH4+ over NO3−, which varied with WFPS (85% > 55% > 70%). This preference decreased for amino acids further in biosynthetic proximity to the transamination step in amino acid biosynthesis. Combined incorporation of NH4+ and NO3− increased total hydrolysable amino acid-N concentration linked to WFPS (55% ∼ 85% > 70%). Incorporation rates of applied 15N showed the same trend as NH4+ preference with WFPS (85% > 55% > 70%), which is related to microbial activity and nutrient mobility. Despite differences in incorporation, when normalised to soil available N, incorporation was comparable in the short-term. Mechanistic control of WFPS via assimilation into the largest soil organic N pool is important to mitigate potential positive feedbacks to N losses and support N supply to plants.
Original languageEnglish
Article number109114
JournalSoil Biology and Biochemistry
Early online date28 Jun 2023
Publication statusPublished - 1 Sept 2023

Bibliographical note

Funding Information:
M.K.R was funded via the UK Natural Environment Research Council Global Challenges Research Fund programme on Reducing the Impacts of Plastic Waste in Developing Countries (NE/V005871/1). N. L. and L. C. were funded by BBSRC ( BB/K001051/1 ) and also thank BBSRC grants BBS/E/C/000I0310 and BBS/E/C/000I0320 . The authors wish to thank the NERC for partial funding of the National Environmental Isotope Facility (NEIF; contract no. NE/V003917/1 ). The authors wish to thank the HEFCE SRIF and the University of Bristol for funding the GC-IRMS capabilities. W. Armstrong is thanked for assistance in amino acid preparation.

Publisher Copyright:
© 2023 The Authors


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