The document discusses nitrous oxide (N2O) emissions from soil and opportunities for mitigation. It notes that N2O concentrations have increased 20% over the last 100 years. Soil is a major source, producing 10.2 Tg N per year. The primary controls of N2O production from soil are nitrogen application, aeration/water content, temperature, and available carbon. Understanding these controls is key for modeling emissions and developing mitigation strategies like improved fertilizer management and planting techniques. New opportunities for mitigation may include manipulating rhizosphere microbes and chemistry to maximize N2O reduction to nitrogen gas.

1. Nitrogen use and climate change mitigation Liz Baggs University of Aberdeen

2. Short History of Nitrous Oxide Joseph Priestley 1775 N 2 O

3. Joseph Priestley 1775 Short History of Nitrous Oxide N 2 O

4. Ode to Nitrous Oxide "Yet are my eyes with sparkling lustre fill'd Yet is my mouth replete with murmuring sound Yet are my limbs with inward transports fill'd And clad with new-born mightiness around." Sir Humphry Davy Presidente de la Royal Society 1820-27 Short History of Nitrous Oxide N 2 O

5. Short History of Nitrous Oxide

6. Short History of Nitrous Oxide

7. Nitrous Oxide is a Potent Greenhouse Gas CO 2 N 2 O CH 4 Carbon Dioxide Methane Nitrous Oxide 20 years 100 years 500 years 1 1 1 62 23 7 275 296 156

8. Atmospheric nitrous oxide has increased by 20% over the last 100 years N 2 O concentrations (IPCC Fourth Assessment Report, 2007)

12. The Nitrogen Cycle NO 3 - N 2 NO 2 - NH 4 + NH 2 OH N 2 O NO D E N I T R I F I C A T I O N N I T R I F I C A T I O N

13. The Nitrogen Cycle NO 3 - N 2 NO 2 - NH 4 + NH 2 OH N 2 O NO D E N I T R I F I C A T I O N FIXATION

14. NO 3 - N 2 NO 2 - NH 4 + NH 2 OH N 2 O NO D E N I T R I F I C A T I O N N I T R I F I C A T I O N FIXATION Cellular toxin Greenhouse gas The Nitrogen Cycle

15. Field & lab experimentation

17. Primary controls of N 2 O production Understanding the controls of N 2 O fluxes is essential for modelling, up-scaling and mitigation

18. Primary controls of N 2 O production N application Understanding the controls of N 2 O fluxes is essential for modelling, up-scaling and mitigation grass arable-cereal arable-non cereal Baggs et al 2000 Soil Use Manage 16, 82-87. Baggs et al 2003 Plant Soil 254, 361-370. Wheat Maize Cabbage Sprouts Mustard Broccoli Sugar beet leaf Grass/clover Bean Lettuce Velthof et al 2002 Baggs et al 2000, 2003

19. Primary controls of N 2 O production Aeration/water content N application Understanding the controls of N 2 O fluxes is essential for modelling, up-scaling and mitigation nitrification denitrification

20. pH Primary controls of N 2 O production Aeration/water content N application Understanding the controls of N 2 O fluxes is essential for modelling, up-scaling and mitigation

21. pH Primary controls of N 2 O production Aeration/water content N application Temperature Temperature ( o C) N 2 O flux (g N 2 O-N ha -1 d -1 ) Understanding the controls of N 2 O fluxes is essential for modelling, up-scaling and mitigation

22. pH Primary controls of N 2 O production Aeration/water content N application Temperature Available C Understanding the controls of N 2 O fluxes is essential for modelling, up-scaling and mitigation 14 days N 2 O N 2

23. N 2 O is produced in several microbial processes NH 3 NH 2 OH NO 2 - NO N 2 O N 2 NO 3 - NO 2 - NO N 2 O N 2 N 2 O Nitrification Denitrification Nitrifier denitrification Nitrate ammonification NH 4 + N 2 O ? 15 N site preference 15 N, 18 O enrichment & natural abundance Which process is contributing to emissions under particular environmental conditions or management? N N O N N co-substrate Co- Recent advances

24. Gross nitrification mg N kg -1 d -1 SRC Willow 12.0 ± 0.6 10 days Miscanthus 7.3 ± 0.3 Sandy loam NH 4 NO 3 at 12 g N m -2 nitrification nitrate reduction Nitrification versus nitrate reduction

25. Denitrifier-N 2 O & N 2 15 N 10 atom %

26. O 2 gradient Air flow controller O 2 analyser C exudate A C exudate B Different denitrifier gene copy numbers? 15 N-N 2 O 15 N-N 2 CuNir, cdNir, NosZ pump Different denitrifier gene copy numbers? N 2 O/O 2 CuNir, cdNir, NosZ CuNir, cdNir, NosZ Lab soil columns

27. Alleviation of Cu-limitation at pH 7? N 2 O:N 2 ? Potential for enhancing N 2 O reduction

29. In situ visualisation of pseudomonads marked with unstable gfp in the rhizosphere of a barley seedling Colonising root tip On root surface Where is C flowing in the rhizosphere?

30. Blue = 28 Si - Green = 12 C 14 N - (represents organic matter) Red = 15 / 14 N ratio images (distribution of 15 N enriched P. fluorescens ) Herrmann et al 2007 Rapid Comm Mass Spec 21, 29-34 Mapping location of active microbes

31. 13 C SOM Hotspots of denitrifier activity (e.g. with C quantity, quality & O 2 availability) N 2 O production & source partitioning in situ. Air filled pore Water filled pore Anoxic zone Oxic zone 15 N & 13 C in denitrifier or 15 N-N 2 O 15 N in denitrifier or 15 N-N 2 O 15 N-NO 3 applied to soil Mapping location of active microbes

32. Manipulating the rhizosphere for function Lower N application 13 C SOM N 2 O N 2 O:N 2 Nitrification + Denitrification Nitrifier denitrification Net CH 4 Inhibition of CH 4 oxidation CH 4 oxidation Distance from root/time High N application Denitrification Lowered nitrifier denitrification Denitrification Plant breeding for exudate C compounds which enhance reduction of N 2 O to N 2 SOM management to alleviate Cu-limitation to enhance reduction of N 2 O to N 2 Lower N 2 O:N 2

33. Future challenge: Resolving issues of scale gene plant field landscape 10 -8 m 10 -2 m 10 2 m 10 5 m Bug to big Modelling

34. Management for mitigation Opportunities for mitigation Controlled release fertilisers. Synchronising N applications & N availability with crop demand. Nitrification inhibitors. Split fertiliser applications. Minimise fallow periods. ‘ Optimise’ tillage. Placement of injection of fertilisers. Large, less frequent irrigation. Mosier 1994 Fert Res 37, 191-200 Mosier et al 1996 Plant & Soil 181, 95-108 Dalal et al 2003 Aust J Soil Res 41, 165-195 Residue management – combined inorganic/organic-N applications.

35. New opportunities for mitigation? Plant breeding for exudate C compounds which maximise reduction of N 2 O to N 2 Application of zeolite + lime 5 μm Nitrosomonas europaea cells attached onto clinoptilolite particles Management for mitigation Biosensor luminescence response to root exudation Paterson et al. J. Exp. Bot. 2006 57:2413-2420 Zaman et al 2007 Aust J Soil Res 45, 543-553

36. Greater understanding of regulation of the N 2 O reductase: mitigation by reducing N 2 O to N 2 ? Greater understanding of interactions with C cycle. Understanding control of microsite structures on microbial community composition & processes. Advancing techniques & adopting interdisciplinary approaches to quantify and understand controls on N 2 O. Tackling issues of scale. Integrating chemostat and soil studies to field/landscape. How can we constrain the soil-N 2 O budget? Enhance quantification and understanding of N 2 O production informing targeted and sustainable management for mitigation

37. The Nitrous Oxide Focus Group is a consortium-based research initiative established to explore the action of the greenhouse gas, Nitrous Oxide; its role in climate change, the role of bacteria in the greenhouse gas emissions and to develop techniques to mitigate its effect. Ultimately the Group will work toward solutions for the wider community and commercial and non-academic partners are being sought to inform and enable the development of opportunities arising from the Nitrous Oxide Focus Group’s research. http://www.nitrousoxide.org/index.html [email_address] [email_address]