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ISOTOPE FRACTIONATION FACTORS ASSOCIATED WITH SOIL DENITRIFICATION

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ISOTOPE FRACTIONATION FACTORS

ASSOCIATED WITH SOIL DENITRIFICATION

- Dominika Lewicka-Szczebak1,2 , Reinhard Well2,
- Laura Cardenas3, Peter Matthews4, Roland Bol3,
- Lena Rohe1
- 1 ThÃ¼nen-Institut, Germany, 2University of Wroclaw, Poland
- 3 Rothamsted Research,UK, 4University of Plymouth, UK,
- 5 Agrosphere Institute, Germany

Introduction ISOTOPE FRACTIONATION FACTORS

DENITRIFICATION PROCESSES

N2O production

N2O reduction

Î²

Î±- position

N2O reduction

SP= Î±-Î²

N

N

O

N

N

N2

preferredconsumption of bondswith

14Nand16O

Îµ

N2O

N

O

N2O production

N

N

O

Îµ

NO

Îµ

differentiationwithinthemolecule

O

O

N

O

Îµ

H

H

NO2-

exchange

of O-isotopes

withsoilwater

Îµ

changeinSP

(SitePreference)

NO3-

N

N

O

Î²

Î±- position

O

Îµ

O

H

H

N

O

O

sum of Îµ â†’ NIE â€“ Net IsotopeEffects â†’ Æž

of 3 independent factors:

Î´15N, Î´18O, SP

N

N

N

N

N

enrichment in 15N

e.g. Æž 15N: -45 - -13â€°

O

O

O

enrichment in 18O

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

Introduction RAYLEIGH EQUATIONS

Î´S- isotopicsignature of substrateinparticular point of thereaction

Î´ S0 - isotopicsignature of substrateprior to initiation of thereaction

f - remainingunreactedfraction

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

(Mariotti et al., 1981)

Î´15N

N2O production

Î´S

NO32-

Î´P

Î·

N2O

Î´S0=0â€°

Î·

remaining nitrate

Introduction RAYLEIGH EQUATIONS

Î´S- isotopicsignature of substrateinparticular point of thereaction

Î´ S0 - isotopicsignature of substrateprior to initiation of thereaction

f - remainingunreactedfraction

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

(Mariotti et al., 1981)

Î´15N

N2O production

+ reduction

Î´S

NO32-

Î´P

Î·

N2O

Î´S0=0â€°

Î·

fred=0.8

fred=0.5

Î´S0

fred=0.2

remaining nitrate

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
- Î´15N, Î´18O of NO3-

Methods / Results MODELING STRATEGY 1

only N2O production

+ known N2O reduction

INPUTS

INPUTS

N2O emission

NO3- consumption

Î´15N, Î´18O of NO3-

Î´15N, Î´18O, SP of N2O

f

unconsumed NO3-

N2O emission

NO3- consumption

Î´15N, Î´18O of NO3-

ÆžP-S of N2O production

Î´15N, Î´18O, SP of N2O

15N (N2), 15N (N2O)

Î´S0

N2O before reduction

Î´S, Î´S0

Î´S

f

unreduced fraction

OUTPUTS

ÆžP-Sof N2Oproduction

OUTPUTS

ÆžP-Sof N2Oreduction

fast rate reaction

Methods EXPERIMENTS DESIGN 2

on-line GC-analyses

1.5h time step

known reduction

amendment

addition

samples for isotopomers analysis

once a day

â€˜DENISâ€™ incubation system

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

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 â€“ high reductionratio

produced SP range:

from -10â€° (bacteria) to 36â€° (fungi)

minimalvalue of Î´18O

ca. 10 â€°

(Ostrom & Ostrom, 2011)

(Snider et al., 2011)

Methods / Results IMPROVED MODELING STRATEGY 2

INPUTS

OUTPUTS

OUTPUTS

INPUTS

pool2 â€“ high reductionratio

I wyniki â€“ Å¼e zaleÅ¼y od tempa procesu, mniejsze/wiÄ™ksze â€“ rÃ³Å¼ne poole

ResultsFIT OF MEASURED AND MODELED DATA

SAT/sat

Î´15N

UNSAT/sat

HALFSAT/sat

DiscussionCONTROLLING FACTORS

15N NIE of production

increasing reactions rates â€“

â€“ smaller fractionation factors

increasing production rate

smaller difference between product and substrate

increasing soil moistureâ€“

â€“ smaller fractionation factors

Îµ - 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.)

DiscussionCONTROLLING FACTORS

15N NIE of reduction

increasing substrate availability â€“

â€“ higher fractionation factors

increasing reduction ratio

higher difference between product and substrate

decreasing soil moistureâ€“

â€“ higher fractionation factors

Îµ - 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)

DiscussionCONTROLLING FACTORS

produced 18O

increasingreactionsratesâ€“

â€“higherÎ´values

â€“ lowerequilibriumwithsoilwater ?

100% WFPS

94% WFPS

85% WFPS

75% WFPS

Conclusions

- Wide range of Net Isotope Effects associated with denitrification N2O production and reductionÆž15N: -43 - -18â€°Æž15N: -9 - -1â€°Î´18O: 10 - 40â€°Æž18O: -20 - -4â€° ÆžSP: -10 - 1â€° ÆžSP: -12 - -2â€°
- 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 - -13â€°

-9 - -5â€°

11 - 24â€°

-20 - -13â€°

-10 - 10â€°

-8 - -3â€°

*

*

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

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

MethodsMODEL CONSTRUCTION

amendment

pool1 emission terminated

POOL1 â€“ fast production,

low reduction

POOL2 â€“ slow production,

high reduction

(Bergstermann et al., 2011)

ResultsFIT OF MEASURED AND MODELED DATA

SAT/sat

SP

UNSAT/sat

HALFSAT/sat

ResultsFIT OF MEASURED AND MODELED DATA

SAT/sat

Î´18O

HALFSAT/sat

UNSAT/sat

N2-free

atmosphere

N

N

N

N

O

O

H

H

O

NO3-

N

O

O

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-