ISOTOPE FRACTIONATION FACTORS
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ISOTOPE FRACTIONATION FACTORS ASSOCIATED WITH SOIL DENITRIFICATION. Dominika Lewicka-Szczebak 1 ,2 , Reinhard Well 2 , Laura Cardenas 3 , Peter Matthews 4 , Roland Bol 3 , Lena Rohe 1 1 Thünen-Institut, Germany, 2 Uni versity of Wroclaw, Poland

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ISOTOPE FRACTIONATION FACTORS ASSOCIATED WITH SOIL DENITRIFICATION

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Isotope fractionation factors associated with soil denitrification

ISOTOPE FRACTIONATION FACTORS

ASSOCIATED WITH SOIL DENITRIFICATION

  • Dominika Lewicka-Szczebak1,2 , Reinhard Well2,

  • Laura Cardenas3, Peter Matthews4, Roland Bol3,

  • Lena Rohe1

  • 1 Thünen-Institut, Germany, 2University of Wroclaw, Poland

  • 3 Rothamsted Research,UK, 4University of Plymouth, UK,

  • 5 Agrosphere Institute, Germany


Isotope fractionation factors associated with soil denitrification

Introduction ISOTOPE FRACTIONATION FACTORS

DENITRIFICATION PROCESSES

N2O production

N2O reduction

β

α- position

N2O reduction

SP= α-β

N

N

O

N

N

N2

preferredconsumption of bondswith

14Nand16O

ε

N2O

N

O

N2O production

N

N

O

ε

NO

ε

differentiationwithinthemolecule

O

O

N

O

ε

H

H

NO2-

exchange

of O-isotopes

withsoilwater

ε

changeinSP

(SitePreference)

NO3-

N

N

O

β

α- position

O

ε

O

H

H

N

O

O

sum of ε → NIE – Net IsotopeEffects → ƞ

of 3 independent factors:

δ15N, δ18O, SP

N

N

N

N

N

enrichment in 15N

e.g. ƞ 15N: -45 - -13‰

O

O

O

enrichment in 18O


Isotope fractionation factors associated with soil denitrification

Introduction OBJECTIVES OF MODELING APROACH

Determination of Net IsotopeEffectsof productionand reduction

Comparison of NIEs for differentreaction dynamics and different experimental conditions

Development of a method to calculate reduction contribution based on isotopomers data


Isotope fractionation factors associated with soil denitrification

Introduction RAYLEIGH EQUATIONS

δS- isotopicsignature of substrateinparticular point of thereaction

δ S0 - isotopicsignature of substrateprior to initiation of thereaction

f - remainingunreactedfraction

ƞP-S- Net IsotopeEffect (NIE) betweenproduct and substrate

(Mariotti et al., 1981)

δ15N

N2O production

δS

NO32-

δP

η

N2O

δS0=0‰

η

remaining nitrate


Isotope fractionation factors associated with soil denitrification

Introduction RAYLEIGH EQUATIONS

δS- isotopicsignature of substrateinparticular point of thereaction

δ S0 - isotopicsignature of substrateprior to initiation of thereaction

f - remainingunreactedfraction

ƞP-S- Net IsotopeEffect (NIE) betweenproduct and substrate

(Mariotti et al., 1981)

δ15N

N2O production

+ reduction

δS

NO32-

δP

η

N2O

δS0=0‰

η

fred=0.8

fred=0.5

δS0

fred=0.2

remaining nitrate


Isotope fractionation factors associated with soil denitrification

Methods EXPERIMENTS DESIGN 1

known reduction

only N2O production

8 variants, 1 water saturation:75 WFPS

C2H2 addition

reduction inhibition

no C2H2

reduction occurs

gas samples

each 2/4/12h

  • GC-analyses N2O

  • isotopomers analysis (15N, 18O, SP in N2O)

  • 15N (N2), 15N (N2O) analysis

soil samples

beginning / end

  • NO3- content

  • δ15N, δ18O of NO3-


Isotope fractionation factors associated with soil denitrification

Methods / Results MODELING STRATEGY 1

only N2O production

+ known N2O reduction

INPUTS

INPUTS

N2O emission

NO3- consumption

δ15N, δ18O of NO3-

δ15N, δ18O, SP of N2O

f

unconsumed NO3-

N2O emission

NO3- consumption

δ15N, δ18O of NO3-

ƞP-S of N2O production

δ15N, δ18O, SP of N2O

15N (N2), 15N (N2O)

δS0

N2O before reduction

δS, δS0

δS

f

unreduced fraction

OUTPUTS

ƞP-Sof N2Oproduction

OUTPUTS

ƞP-Sof N2Oreduction

fast rate reaction


Isotope fractionation factors associated with soil denitrification

Methods EXPERIMENTS DESIGN 2

on-line GC-analyses

1.5h time step

known reduction

amendment

addition

samples for isotopomers analysis

once a day

‘DENIS’ incubation system

3 water saturations: 100 WFPS, 94 WFPS, 85 WFPS


Isotope fractionation factors associated with soil denitrification

Methods / Results MODELING STRATEGY 2

known N2O reduction

INPUTS

found by itinerations to reachthebest fit betweenmodeled and measuredvalues

(Rock et al., 2011)

OUTPUTS

(Well & Flessa, 2009)

pool2 – high reductionratio

produced SP range:

from -10‰ (bacteria) to 36‰ (fungi)

minimalvalue of δ18O

ca. 10 ‰

(Ostrom & Ostrom, 2011)

(Snider et al., 2011)


Isotope fractionation factors associated with soil denitrification

Methods / Results IMPROVED MODELING STRATEGY 2

INPUTS

OUTPUTS

OUTPUTS

INPUTS

pool2 – high reductionratio

I wyniki – że zależy od tempa procesu, mniejsze/większe – różne poole


Isotope fractionation factors associated with soil denitrification

ResultsFIT OF MEASURED AND MODELED DATA

SAT/sat

δ15N

UNSAT/sat

HALFSAT/sat


Isotope fractionation factors associated with soil denitrification

DiscussionCONTROLLING FACTORS

15N NIE of production

increasing reactions rates –

– smaller fractionation factors

increasing production rate

smaller difference between product and substrate

increasing soil moisture–

– smaller fractionation factors

ε - FRACTIONATION FACTORS

K - PROCESS RATES

increasing

water content

enzymatic

reaction

diffusion into cell

enzyme

activity

diffusion

diffusion

out of cell

100% WFPS

94% WFPS

85% WFPS

75% WFPS

(Farquar et al., 1982;

Ostrom & Ostrom, 2011; Well et al., acc.)


Isotope fractionation factors associated with soil denitrification

DiscussionCONTROLLING FACTORS

15N NIE of reduction

increasing substrate availability –

– higher fractionation factors

increasing reduction ratio

higher difference between product and substrate

decreasing soil moisture–

– higher fractionation factors

ε - FRACTIONATION FACTORS

K - PROCESS RATES

enzymatic

reaction

diffusion into cell

enzyme

activity

diffusion

diffusion

out of cell

unreduced fraction

increasing substrate availability

(Jinuntuya-Nortman et al., 2008, Ostrom & Ostrom, 2011)


Isotope fractionation factors associated with soil denitrification

DiscussionCONTROLLING FACTORS

produced 18O

increasingreactionsrates–

–higherδvalues

– lowerequilibriumwithsoilwater ?

100% WFPS

94% WFPS

85% WFPS

75% WFPS


Isotope fractionation factors associated with soil denitrification

Conclusions

  • Wide range of Net Isotope Effects associated with denitrification N2O production and reductionƞ15N: -43 - -18‰ƞ15N: -9 - -1‰δ18O: 10 - 40‰ƞ18O: -20 - -4‰ ƞSP: -10 - 1‰ ƞSP: -12 - -2‰

  • The magnitude of isotope effects is controlled by several factorshigher NIEs when lower reactions rates, higher substrate availability, more efficient substrate transportation (e.g. lower soil moisture)

  • Modelling aproach provides promising results for future development of a method to calculate reduction contribution based on isotopomers data

-45 - -13‰

-9 - -5‰

11 - 24‰

-20 - -13‰

-10 - 10‰

-8 - -3‰

*

*

*previous literature data (Well & Flessa, 2009; Ostrom & Ostrom, 2011)


Isotope fractionation factors associated with soil denitrification

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

N

N

N

N

O

THANK YOU FOR YOUR ATTENTION

  • This research was funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC) with competitive grants BB/E001580/1 and BB/E001793/1 and by Deutsche Forschungsgemeinschaft (DFG) WE-1904-4.

  • The first authoris suppored by the Foundation for Polish Science.

  • DominikaLewicka-Szczebak


Isotope fractionation factors associated with soil denitrification

MethodsMODEL CONSTRUCTION

amendment

pool1 emission terminated

POOL1 – fast production,

low reduction

POOL2 – slow production,

high reduction

(Bergstermann et al., 2011)


Isotope fractionation factors associated with soil denitrification

ResultsFIT OF MEASURED AND MODELED DATA

SAT/sat

SP

UNSAT/sat

HALFSAT/sat


Isotope fractionation factors associated with soil denitrification

ResultsFIT OF MEASURED AND MODELED DATA

SAT/sat

δ18O

HALFSAT/sat

UNSAT/sat


Isotope fractionation factors associated with soil denitrification

N2-free

atmosphere

N

N

N

N

O

O

H

H

O

NO3-

N

O

O


Isotope fractionation factors associated with soil denitrification

N

N

N

N

O

N

N

O

C

glucose

15NO3-

O

N

O

O

O

N

C

glucose

O

O

NO3-

O

15NO3-

N

O

O

O

N

O

O

NO3-


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