Project highlights

  • Elucidating the molecular mechanisms behind microbial production of HONO. 
  • Quantifying the effects of HONO on soil organic matter turnover and composition. 
  • Linking HONO emissions with soil carbon storage and global climate models. 

Overview

This project explores the hidden role of biogenic nitrous acid (HONO) in soil biogeochemistry and its significant implications for both carbon and nitrogen cycling. HONO, a key precursor for hydroxyl radicals (OH), plays a crucial role in atmospheric chemistry by influencing the oxidative capacity of the atmosphere (Su et al., 2011). Despite its importance, the microbial sources of HONO in soil remain poorly understood. This project focuses on understanding the mechanisms behind HONO production, particularly by ammonia-oxidising bacteria (AOB) and archaea (AOA), two microbial groups that are central to nitrogen cycling in soils (Kuypers et al., 2018). 

By conducting a series of controlled experiments using isolated AOA and AOB cultures, the project aims to test the hypothesis that AOB are major contributors to HONO emissions, while AOA play a lesser or negligible role. These experiments will investigate how different environmental factors, such as ammonia concentration, pH, oxygen levels, and temperature, affect HONO production. This work will provide novel insights into the biochemical pathways responsible for HONO release from soils. 

Beyond its production, HONO has the potential to accelerate the breakdown of soil organic matter (SOM), making it a key player in the carbon cycle. HONO’s high reactivity can stimulate photooxidation of complex soil organic compounds, thereby enhancing soil carbon turnover rates (Stemmler et al., 2006). This project will quantify the effects of HONO on SOM composition and degradation, exploring how these processes might link soil nitrogen and carbon cycles more closely than previously understood. 

The project leverages advanced analytical techniques, such as isotope labelling, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), to investigate these complex interactions at both the microbial and chemical levels. The findings are expected to fill critical gaps in current Earth system models, particularly in terms of predicting soil emissions of reactive nitrogen and their effects on soil carbon storage and climate change (Weber et al., 2015).

Host

University of Warwick

Theme

  • Organisms and Ecosystems
  • Dynamic Earth

Supervisors

Project investigator

Co-investigators

How to apply

Methodology

The project will employ a combination of controlled laboratory experiments and advanced analytical techniques to investigate HONO production in soils. Using isolated cultures of ammonia-oxidising bacteria (AOB) and archaea (AOA), we will measure HONO emission rates under varying environmental conditions, including changes in ammonia concentration, pH, oxygen levels, and temperature. Soil incubations will further explore these processes in more complex, real-world systems. Spectroscopic techniques, such as X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, will be used to characterise the chemical composition of soil organic matter (SOM) and track changes in nitrogen species resulting from HONO exposure (Lehmann et al., 2005). Isotope labelling will provide additional precision in quantifying the sources of HONO (Ermel et al., 2018). 

Training and skills

DRs will be awarded CENTA Training Credits (CTCs) for participation in CENTA-provided and ‘free choice’ external training. One CTC can be earned per 3 hours training, and DRs must accrue 100 CTCs across the three and a half years of their PhD.  

The DR will receive interdisciplinary training across environmental microbiology, biogeochemistry, and analytical chemistry. They will gain expertise in advanced techniques like isotope labelling, spectroscopic instrumentation, and microbial cultivation. The project will involve state-of-the-art facilities at the University of Warwick, and the DR will participate in CENTA training workshops to develop transferable skills such as data analysis, scientific communication, and project management. 

Further details

You can visit out lab website: ryanmushinski.com. Feel free to contact Ryan (Ryan.M[email protected]) with any questions. 

To apply to this project:  

  • You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities.  

 Applications must be submitted by 23:59 GMT on Wednesday 8th January 2025.  

Possible timeline

Year 1

Initial experiments with AOA and AOB cultures to measure HONO production under varied conditions.

Year 2

Investigation of HONO’s effects on soil organic matter using spectroscopic techniques.

Year 3

Field experiments and integration of data into climate models.

Further reading

Ermel, M. et al. (2018). Hydroxylamine released by nitrifying microorganisms is a precursor for HONO emission from drying soils. Scientific Reports, 8(1), p. 1877. 

Kuypers, M.M.M., Marchant, H.K. and Kartal, B. (2018). The microbial nitrogen-cycling network. Nature Reviews Microbiology, 16(5), pp. 263–276. 

Lehmann, J. et al. (2005). Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy for mapping nano-scale distribution of organic carbon forms in soil. Global Biogeochemical Cycles, 19(1). 

Stemmler, K. et al. (2006). Light induced conversion of nitrogen dioxide into nitrous acid on submicron humic acid aerosol. Atmospheric Chemistry and Physics, 6(9), pp. 2569–2579. 

Su, H. et al. (2011). Soil Nitrite as a Source of Atmospheric HONO and OH Radicals. Science, 333(6049), pp. 1616–1618. 

Weber, B. et al. (2015). Biological soil crusts accelerate the nitrogen cycle through large NO and HONO emissions in drylands. Proceedings of the National Academy of Sciences, 112(50), pp. 15384–15389.