- Agriculture is a major source of nitrogen gases, which impact climate
- You will assess how common agricultural practices influence soil emissions of an understudied group of nitrogen trace gases (NOz) along a gradient of soil carbon and nitrogen.
- You will explore soil microbiomes in agricultural systems to uncover correlations between community structure and NOz emissions as well as investigate novel intersections between carbon- and nitrogen-cycle processes
A range of pollutant gases, and especially nitrogen (N) compounds (N2O, NO, NO2, etc.) are emitted to the atmosphere from agricultural activities.1 These gases are extremely important for a myriad of reason including their contribution to climate change, urban air pollution, and N-deposition. Common agricultural practices such as fertilization and irrigation 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. This project aims to better quantify N-gas fluxes from agricultural systems as well as map the various mechanisms associated with emission and consumption in soil.
The N-cycle is a significant source of atmospheric N-gases; however, the conditions leading to both emission and consumption are extremely complex. This is particularly true for the suite of NOz gases (HONO, HNO3, organic nitrates, and particulate nitrates), which are much less studied than N2O, NO, and NO2, but represent an important driver of climate via their contribution to the oxidizing capacity of the atmosphere. Additionally, there are potential intersections between N-cycling microbes and those involved in carbon-cycling, which may affect transformations of N in the soil. For example, N-cycle products (e.g., NH2OH and NO) can react extracellularly with reactive oxygen species (ROS = OH, O2¯, HO2, H2O2) generated by heterotrophic microbes to produce reactive N compounds such as nitrite and NO2. These types of understudied reactions in soil represent a major gap in our understanding of the N-cycle which prevents us from scaling these processes to the regional and global scales. This proposed study will explore how various agricultural crops and practices found throughout the UK influence the production of N-gases and systematically evaluate the processes responsible for emissions.
Results will allow the student to establish correlations between gas flux potentials on specific crops, fertilizer, soil carbon, ROS production rates, and microbial indicators. These along with soil physicochemical properties such as soil pH, water content, and O2 availability will allow the student to parameterize N-gas fluxes from agricultural activity in Earth system models.
The approach will be to couple microbiological analysis to field-based measurements taken from the University of Warwick – Wellesbourne Campus. The student will target major crops (i.e., wheat, sugar beet, and potato), each of which will have a N fertilization gradient from low to high as well as two soil carbon content treatments via till vs. no-till. Field-based fluxes of NO, NO2, N2O, 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. These samples will also be subjected to amplicon (16S and ITS) and metagenomic sequencing to identify changes in microbial community composition and functional potential, respectively. Additional microcosm studies will further allow the student to vary other edaphic conditions to evaluate reaction mechanisms (e.g., soil water content, oxic vs. O2-free, and sterilized vs. unsterilized soil).
Training and Skills
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 from soil and subsequent quantification, and building sampling microcosms). Field-based cultivation and management of agricultural crops will also be emphasized.
Year 1: Quantify production of N-gases (especially NOz) along gradients of soil N and carbon in agricultural systems.
Year 2: Use culture-dependent and -independent methods to identify soil microbiomes, specifically focusing on heterotrophic microbes that produce extracellular ROS as well as N-cycle taxa.
Year 3: Explore how N-cycle intermediates and products (e.g, NO and NH2OH) react extracellularly with ROS produced by heterotrophic bacteria and fungi to form various reactive N products.
Partners and collaboration (including CASE)
Both Dr. Mushinski and Professor Bending have substantial expertise in nitrogen cycle biogeochemistry as well as plant-soil-microbe interactions, evidenced by publications in the Proceedings of the National Academy of Sciences, New Phytologist, and Soil Biology and Biochemistry.
Dr. Ryan M. Mushinski
School of Life Sciences
University of Warwick
Current email: firstname.lastname@example.org