I Danksagung ................................................. IV
II Zusammenfassung ............................................ VI
III Summary ................................................... VII
IV List of Tables ............................................. IX
V List of Figures ............................................. X
VI List of abbreviations and units ........................... XIV
VII Appendix ................................................. XVII
1 Introduction and objectives .................................. 1
2 The process of codenitrification ............................. 4
2.1 Biochemical fundamentals ................................ 4
2.1.1 Formation of hybrid N20 and hybrid N2 by
abiotic N-nitrosation reactions .................. 4
2.1.2 Biotic N-nitrosation due to an enzymatic
catalysis ........................................ 6
2.1.3 The dual character of denitrification ............ 7
2.2 Reports on microbial formation of N20 and N2 by
codenitrification ...................................... 12
2.2.1 Formation of N2O ................................ 12
2.2.2 Formation of N2 ................................. 20
2.3 Controlling factors of codenitrification ............... 22
2.3.1 02 availability ................................. 22
2.3.2 pH value ........................................ 22
2.3.3 Respiratory substrates .......................... 23
2.3.4 Type and kinetic of nucleophiles ................ 24
2.3.5 Physiology of denitrifying species .............. 25
3 15N-aided online determination of soil N2 and N20 release
on a laboratory scale ....................................... 28
3.1 Abstract ............................................... 28
3.2 Introduction ........................................... 28
3.3 Material and Methods ................................... 30
3.3.1 Basic principle of flux determination ........... 30
3.3.2 Instrumental set-up ............................. 31
3.3.1 Flux measurement ................................ 32
3.3.4 Flux calculation ................................ 33
3.3.5 Soil treatment and incubation ................... 35
3.4 Results ................................................ 36
3.4.1 Validation of N2 capturing by Köstrolith SX6® ... 36
3.4.2 Validation of l4N160 interference on N2 flux
determination ................................... 37
3.4.3 N-fluxes, soil moisture, and soil nitrate of
incubated soil aggregates ....................... 39
3.5 Discussion ............................................. 41
3.5.1 N2 flux determination by a 15N aided gas flow
soil core system with an artificial
atmosphere ...................................... 41
3.5.2 Some aspects of N-transformation in soil
aggregates gained by the present approach ....... 43
3.6 Conclusions ............................................ 44
4 A novel 15N tracer model for studying hybrid N2
formation due to anammox or codenitrification ............... 45
4.1 Abstract ............................................... 45
4.2 Introduction ........................................... 45
4.3 Derivation of mathematical expressions ................. 48
4.3.1 Fundamentals .................................... 48
4.3.2 Comprehensive approach .......................... 51
4.3.3 Simplified approach ............................. 52
4.4 Results and discussion ................................. 53
4.4.1 General applicability of derived mathematical
expressions ..................................... 53
4.4.2 Major critical aspects of application ........... 54
4.4.3 Application in case of denitrification and
codenitrification within soils .................. 57
4.5 Conclusions ............................................ 59
5 Formation of hybrid N20 in a suspended soil due to
codenitrification of NH2OH .................................. 61
5.1 Abstract ............................................... 61
5.2 Introduction ........................................... 61
5.3 Materials and Methods .................................. 63
5.3.1 Soil treatment and incubation ................... 63
5.3.2 15N20 and 15N2 determination ..................... 64
5.3.3 15N calculations ................................ 65
5.4 Results ................................................ 67
5.4.1 15NO3 treatment (Experiment I) .................. 67
5.4.2 15NH20H treatments (Experiment II and III) ....... 68
5.4.3 15N03 + NH2OH treatments (Experiment IV
and V) .......................................... 70
5.5 Discussion ............................................. 74
5.5.1 Hybrid N20 due to codenitrification of NH2OH .... 74
5.5.2 Considerations on NH2OH utilization as
quantified by the 15N tracer model .............. 76
5.6 Conclusions ............................................ 78
5.7 Appendix ............................................... 79
5.7.1. Introducing Rbinom as characteristic factor of
hybrid N-N gas formation ........................ 79
6 Concluding discussion ....................................... 85
6.1 15N-aided analysis of hybrid N2O/N2 formation by
codenitrification ...................................... 85
6.2 Considerations on codenitrification in the biosphere ... 88
6.2.1 Terrestrial environments ........................ 88
6.2.2 Aquatic environments ............................ 91
6.2.3 Nitrogen immobilisation due to biotic
nitrosation ..................................... 93
7 References .................................................. 96
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