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Microbial Biogeochemistry of Pollutant Nitrogen Oxides

Primary Supervisor: Dr Ryan Mushinski, School of Life Sciences

Secondary supervisor: Professor Gary Bending

PhD project title: Microbial Biogeochemistry of Pollutant Nitrogen Oxides

University of Registration: University of Warwick

Project outline

A range of pollutant gases, and especially nitrogen (N) compounds (N2O, NO, NO2, etc.) are emitted to the atmosphere from agricultural activities. These gases are extremely important for myriad of reasons including their contribution to climate change, urban air pollution, and N-deposition. Common agricultural practices such as fertilization will continue to increase, likely resulting in high emissions. However, N-gas forecasts from agricultural lands are hampered by (1) a lack of field-based measurements and (2) an incomplete understanding of the processes associated with production and consumption of these gases. Additionally, efforts are currently being made to increase carbon (C) storage in soil, which may have direct consequences on emissions of atmospherically-relevant gases. This project aims to better quantify N-gas fluxes from agricultural systems as well as map the connectedness of soil C and N cycling in relation to gas emissions.

In this project we aim to:

  1. Quantify reactive N-gas emissions along gradients of soil N and C in agricultural systems.
  2. Use culture-dependent and -independent methods to identify agricultural soil microbiomes, specifically focusing on heterotrophic microbes that produce extracellular reactive oxygen as well as N-cycle taxa.
  3. Explore how N-cycle intermediates and products (e.g, NO and NH2OH) react extracellularly with reactive oxygen produced by heterotrophic bacteria and fungi to form various reactive N products.

The approach will be to couple microbiological analysis and microcosm experiments to field-based measurements taken from the University of Warwick – Wellesbourne Campus. Common agricultural crops (e.g. maize, wheat, root vegetables, etc.) will be planted in differing soil N fertilization concentrations (ambient and high) as well as two soil carbon content treatments via additions of high C:N substrate (e.g., sawdust). The factorial nitrogen and carbon amendments will serve to unravel the connectedness of C- and N-cycling in the production of reactive N-gases, hopefully stimulating high abundance of key microbial taxa responsible for ROS and N-cycling activity. Field-based fluxes of NO, NO2, and NOz will be measured, while soil ROS and N-cycle rates will be measured from sampled soil to allow for the establishment of predictive relationships between these variables and to provide evidence for the role of ROS in reactive N production. Additional microcosm studies will further allow us to manipulate other edaphic conditions to evaluate reaction mechanisms (e.g., water content, oxic vs. oxygen-free, soil sterilization).

The following papers are good primers on nitrogen gas emissions.

  1. Robertson GP, et al. 2000. Greenhouse Gases in Intensive Agriculture: Contributions of Individual Gases to the Radiative Forcing of the Atmosphere. Science 289: 1922-1925.
  2. Hudman, R. C. et al. 2012. Steps towards a mechanistic model of global soil nitric oxide emissions: implementation and space based-constraints. Atmospheric Chemistry & Physics 12: 7779-7795. 
  3. Mushinski RM et al. 2019. Microbial mechanisms and ecosystem flux estimation for aerobic NOy emissions from deciduous forest soils. PNAS 116: 2138-2145.

BBSRC Strategic Research Priority: Sustainable Agriculture and Food: Plant and Crop Science. Understanding the Rules of Life: Microbiology & Soil Science

    Techniques that will be undertaken during the project:

    Training during this fellowship includes a wide range of molecular techniques and analyses (microbial culturing, DNA extraction from soil, PCR, sequencing, and bioinformatics) as well as analytical chemistry (nitrogen oxide quantification, reactive oxygen extraction and subsequent quantification, and building sampling microcosms). Field-based cultivation and management of agricultural crops will also be emphasized.

    Contact: Dr Ryan Mushinski, University of Warwick