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Towards a mechanistic understanding of peatland reactive nitrogen cycling


Project Description

Project Highlights:
• Peatlands act as large reservoirs of organic matter; however, environmental change processes, such as increased atmospheric nitrogen deposition, may lead to large emissions of greenhouse and trace gases from these ecosystems.
• In this project, you will quantify emissions of a rarely studied group of trace gases (reactive nitrogen oxide; NOy) from peatlands
• You will use laboratory mesocosms to assess the impact of atmospheric nitrogen deposition on peatland nitrogen cycling
• You will use molecular and biogeochemical techniques to determine if iron-mediated microbial processes are a key source of NOy from peatlands

Overview:
Peatlands in the UK account for 9.5% of land cover1 and are currently experiencing rapid modifications in response to environmental stimuli such as increased atmospheric nitrogen (N) deposition sourced from human activity. These ecosystems perform a plethora of functions, none more critical than acting as large reservoirs of organic matter (OM). Research has focused on how processes such as N-deposition may transform these OM stocks into sources of greenhouse gases. These studies demonstrate a stimulatory effect of N-deposition on CO2 and CH4 emissions2; however, much less attention has been paid to changes in N-cycling associated with enhanced N-deposition.
Net rates of N-cycle processes such as nitrification and denitrification are quite slow in peatlands. In fact, these process account for less than 5% of N removal from these ecosystems.3 However, a different group of N-gases, the reactive nitrogen oxides (NOy = NO, NO2, HONO), are greatly understudied and may actually be emitted at high rates from peatlands, especially under increased N-deposition. NOy gases are categorized as air pollutants causing respiratory distress in humans and are also atmospherically relevant in that they control the oxidative capacity of the atmosphere, the lifetime of greenhouse gases, and the rate of secondary aerosol formation that directly and indirectly affects climate.
While NOy have been shown to be products of nitrification and denitrification, an under-investigated process involving iron (Feammox) may be extremely important in the cycling of N and subsequent production of NOy in these ecosystems. Feammox is a microbial process that generally occurs under anoxic conditions of saturated soils such as peatlands, where iron oxides can act as an electron acceptor and play a critical role influencing N reactions in the absence of oxygen. However, there has been little research exploring whether this reaction results in NOy production.
Thus, there is a critical need to (1) determine the intrinsic ability of UK peatlands to produce NOy, (2) explore the influence of N-deposition on N-cycle rates in these ecosystems, and (3) differentiate the mechanisms by which N is transformed in peatlands, paying particular attention to microbe-iron mediate processes.

Methodology:
We will make seasonal field-based measurements of NOy emissions from minerotrophic fens and ombrotrophic bogs throughout the UK over the course of one year. Both fens and bogs will be studied due to differences in water sources (inflow vs. atmospheric) and physicochemical properties (mineralogy, nutrients, pH). This will allow for a better determination of NOy flux mechanisms. In conjunction, we will establish laboratory mesocosms by taking intact cores from these same sites and analyse potential emissions of NOy from peatlands under differential N-addition amendments. Peatland soil will also be used to quantify the nitrogen-cycling microbial community as well as how it changes over the course of N addition. Soil–iron content will be analysed to determine any potential correlation with NOy production.

Training and skills:
Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.
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 mesocosms). Field-based sampling and measurements from peatland ecosystems will also be emphasized.
Partners and collaboration:
Both Dr. Mushinski and Professor Bending have substantial expertise in nitrogen cycle biogeochemistry as well as soil-microbe interactions, evidenced by publications in the Proceedings of the National Academy of Sciences, New Phytologist, and Soil Biology and Biochemistry. The UK Centre for Ecology and Hydrology (CEH) may be an avenue for partnership on this project.

Funding Notes

This funding provides full tuition fees at the Home/EU rate, pays an annual stipend in line with UK Research Councils (currently £15,009) and a research training support grant (RTSG) of £8,000

References

Further reading:
[1] Bain, C.G. et al. (2011) ‘IUCN UK Commission of Inquiry on Peatlands’, IUCN UK Peatland Programme, Edinburgh.
[2] Bragazza, L. et al. (2006) ‘Atmospheric nitrogen deposition promotes carbon loss from peat bogs’, Proceedings of the National Academy of Sciences 103: 19386–19389.
[3] Hill, B.H. et al. (2016) ‘Comparisons of soil nitrogen mass balances for an ombrotrophic bog and a minerotrophic fen in northern Minnesota’, Science of the Total Environment 550: 880–892.

Related Subjects

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FTE Category A staff submitted: 12.60

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