Nitrogen use and climate change mitigation

Liz BaggsUniversity of Aberdeen

Joseph Priestley1775

N2O

Short History of Nitrous Oxide

Joseph Priestley1775

N2O

Short History of Nitrous Oxide

N2O

Ode to Nitrous Oxide"Yet are my eyes with sparkling lustre fill'd

Yet is my mouth replete with murmuring soundYet are my limbs with inward transports fill'd And clad with new-born mightiness around."

Sir Humphry DavyPresidente de la Royal Society 1820-27

Short History of Nitrous Oxide

Short History of Nitrous Oxide

Short History of Nitrous Oxide

Nitrous Oxide is a Potent Greenhouse Gas

20 years

100 years

500 years

1 1 1

62 23 7

275 296 156

CO2

N2O

CH4

Carbon Dioxide

Methane

Nitrous Oxide

Atmospheric nitrous oxide has increased by 20% over the last 100 years

N2O concentrations (IPCC Fourth Assessment Report, 2007)

Soil is a significant source of N2O

10.2 Tg N y-1

Source: IPCC (2007)

IPCC 2007: ‘Land surface properties and land-atmosphere interactionsthat lead to radiative forcing are not well quantified’.

Upturn in N2O production due toincreases in soil N availability:

•N deposition•N fertilization

NO3-

N2

NO2-

NH4+

NH2OH

N2O

NO

DENITRIFICATION

NITRIFICATION

The Nitrogen Cycle

NO3-

N2

NO2-

NH4+

NH2OH

N2O

NO

DENITRIFICATION

FIXATIO

N

The Nitrogen Cycle

NO3-

N2

NO2-

NH4+

NH2OH

N2O

NO

DENITRIFICATION

NITRIFICATION

FIXATIO

N

Cellular toxin

Greenhouse gas

The Nitrogen Cycle

Field & lab experimentation

•spatially and temporally heterogeneous •Interactions between microbiology, environment & biogeochemistry •wide range of scales

Soil: A complex environment

Primary controls of N2O production

Understanding the controls of N2O fluxes is essential for modelling, up-scaling and mitigation

Primary controls of N2O production

grass arable-cereal arable-non cerealBaggs et al 2000 Soil Use Manage 16, 82-87.

Baggs et al 2003 Plant Soil 254, 361-370.

% r

esid

ue N

em

itte

d a

s N

2O

0

1

2

3

4

5

6

7

Wheat

Maiz

eC

abbage

Spro

uts

Must

ard

Bro

ccoli

Sugar

beet

leaf

Gra

ss/c

lover

Bean

Lett

uce

Velthof et al 2002Baggs et al 2000, 2003

N application

Understanding the controls of N2O fluxes is essential for modelling, up-scaling and mitigation

Primary controls of N2O production

Aeration/water content

N application

Understanding the controls of N2O fluxes is essential for modelling, up-scaling and mitigation

% WFPS

20 40 60 80 100

N2O

pro

duc

tion

nitrification

denitrification

pH

Primary controls of N2O production

Aeration/water content

N application

mg

N2O

-N m

-2 4

1d-1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Denitrification

Nitrification

Denitrification

Nitrification

pH 4.5 pH 7

Understanding the controls of N2O fluxes is essential for modelling, up-scaling and mitigation

pH

Primary controls of N2O production

Aeration/water content

N application

Temperature

Temperature (oC)

N2O

flu

x (g

N2O

-N h

a-1 d

-1)

Understanding the controls of N2O fluxes is essential for modelling, up-scaling and mitigation

pH

Primary controls of N2O production

Aeration/water content

N application

Temperature

Available C

Total organic C (mg C kg-1)100 110 120 130 140 150 160

Den

itri

fier

15N

-N2O

flux

(mg

15N

-N2O

m-2

d-1

)

-50

0

50

100

150

200

250

300

0.0

0.1

0.2

0.3

0.4

0.5

mg

15N

-N2O

m-2

14d

0

20

40

60

80

100control

glucose

mannitol

oxalic acid

mg

15N

-N2 m

-2 1

4d

14 days N2O N2

Understanding the controls of N2O fluxes is essential for modelling, up-scaling and mitigation

N2O is produced in several microbial processes

NH3 NH2OH NO2- NO N2O N2

NO3-

NO2- NO N2O N2

N2O

Nitrification Denitrification

Nitrifier denitrification

Nitrate ammonification

NH4+

N2O

?

15N site preference

15N, 18O enrichment & natural abundance

Which process is contributing to emissions under particular environmental conditions or management?

NNO NN

co-substrateCo-

Recent advances

Miscanthus Willow

N2O

-N (

µg

N m-2

)

0

50

100

150

200

250

300

DenitrificationNitrification

Miscanthus Willow

N2O

-N (

µg

N m-2

)

0

20

40

60

80

100

120

Gross nitrification mg N kg-1 d-1

SRC Willow 12.0 ± 0.6

10 days

Miscanthus 7.3 ± 0.3

Sandy loamNH4NO3 at 12 g N m-2

nitrification

nitrate reduction

Nitrification versus nitrate reduction

Day of year (2001)

170 175 180 185 190 195

Den

itri

fied

15N

-N2O

+ 1

5N

-N2 fl

ux

(mg

N m

-2 d

-1)

0

10

20

30

40

50

36 Pa60 Pa

Rai

nfal

l (m

m)

1612

840

Air

tem

p (o

C)

12

16

20

24

Denitrifier-N2O & N2

15N10 atom %

Day of year (2001)

170 175 180 185 190 195

N2 :N

2O

rat

io

0

100

200

300

400

500

36 Pa

60 Pa

O2 g

rad

ien

tAir

flow controller

O2 analyser

C exudate A C exudate BD

iffe

ren

t d

en

itrifi

er

ge

ne

co

py

nu

mb

ers

?

15N-N2O15N-N2

CuNir, cdNir, NosZ

pump

Diffe

ren

t de

nitrifie

r g

en

e co

py n

um

be

rs?

N2O/O2

CuNir, cdNir, NosZ

CuNir, cdNir, NosZ

Lab soil columns

mg

15N

-N2O

m-2

41d

-1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Nitrification Denitrification

pH 4.5 pH 7.0

0

1

2

3

4

5

6

7

15 mg Cu kg-1 soil60 mg Cu kg-1 soil

g N

2O-N

m-2

7 d-1

Alleviation of Cu-limitation at pH 7?

N2O:N2?

Potential for enhancing N2O reduction

0.0

0.1

0.2

0.3

0.4

0.5

mg

15N

-N2O

m-2

14d

0

20

40

60

80

100control

glucose

mannitol

oxalic acid

mg

15N

-N2 m

-2 1

4d

Common exudation compounds from Ectomycorrhizal fungi.

K15NO3, 5 g N m-2, 10 atom % excess 15N.3.6 g C l-1

14 days

Does C influence N2O reduction?

70% WFPS

N2O N2

Differences in regulation of NO & N2O 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 = 28Si- Green = 12C14N- (represents organic matter) Red = 15/14N ratio images (distribution of 15N enriched P. fluorescens)

Herrmann et al 2007 Rapid Comm Mass Spec 21, 29-34

Mapping location of active microbes

13C

SOM

Hotspots of denitrifier activity (e.g. with C quantity, quality & O2 availability)

N2O production & source partitioning in situ.

Air filled pore

Water filled pore

Anoxic zone

Oxic zone15N & 13C in denitrifieror 15N-N2O

15N in denitrifieror 15N-N2O

15N-NO3 applied to soil

Mapping location of active microbes

Manipulating the rhizosphere for function

Lower N application

13C SOM

N2O N2O:N2

Nitrification + DenitrificationNitrifier denitrification

NetCH4

Inhibition of CH4 oxidationCH4 oxidation

Distance from root/time

High N application

Denitrification

Lowered nitrifier denitrification

DenitrificationPlant breeding for exudate C compounds which enhance reduction of N2O to N2

SOM management to alleviate Cu-limitation to enhance reduction of N2O to N2

Lower N2O:N2

Future challenge: Resolving issues of scale

gene

plant

field

landscape

10-8 m

10-2 m

102 m

105 m

Bug to big

Mo

de

l ling

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, 191-200Mosier 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 N2O to N2

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 2007Aust J Soil Res 45, 543-553

Greater understanding of regulation of the N2O reductase: mitigation by reducing N2O to N2?

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 N2O.

Tackling issues of scale. Integrating chemostat and soil studies to field/landscape.

How can we constrain the soil-N2O budget?

Enhance quantification and understanding of N2O 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.htmld.richardson@uea.ac.uke.baggs@abdn.ac.uk