Nitrogen use and climate change mitigation Liz Baggs University of Aberdeen
Short History of Nitrous Oxide Joseph Priestley 1775 N 2 O
Joseph Priestley 1775 Short History of Nitrous Oxide N 2 O
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
Soil is a significant source of N 2 O 10.2 Tg N y -1 Source: IPCC (2007) IPCC 2007: ‘Land surface properties and land-atmosphere interactions that lead to radiative forcing are not well quantified’.
Upturn in N 2 O production due to
increases in soil N availability:
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
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
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
Interactions between microbiology, environment & biogeochemistry
wide range of scales
Soil: A complex environment
Primary controls of N 2 O production Understanding the controls of N 2 O fluxes is essential for modelling, up-scaling and mitigation
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
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
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
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
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
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
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
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
Alleviation of Cu-limitation at pH 7? N 2 O:N 2 ? Potential for enhancing N 2 O reduction
Common exudation compounds from Ectomycorrhizal fungi.
K 15 NO 3 , 5 g N m -2 , 10 atom % excess 15 N.
3.6 g C l -1 14 days Does C influence N 2 O reduction? 70% WFPS N 2 O N 2 Differences in regulation of NO & N 2 O reductases? Preference for different C compounds in rhizosphere denitrifier community?
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?
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
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
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
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
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.
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
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
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]