Contents ........................................................ I
List of Tables .................................................. V
List of Figures ............................................... VII
List of Abbreviations ........................................... X
Kurzzusammenfassung .......................................... XIII
Abstract ...................................................... XIV
Extended Summary ................................................ 1
1 General Introduction ......................................... 3
1.1 Carbon sequestration in terrestrial ecosystems .......... 3
1.2 Dynamics of soil organic matter: Functional SOM pools
and SOM stabilisation ................................... 4
1.3 SOM, a substrate for soil microorganisms and plant -
soil feedback loops ..................................... 7
2 BIOLOG - Europe Programme: The DIVA subproject ............... 8
3 Main aims of this thesis ..................................... 9
4 Study area and sampling design .............................. 12
4.1 Site description ....................................... 12
4.2 Experimental and sampling design ....................... 13
5 General Methods ............................................. 13
5.1 General soil and vegetation analysis ................... 13
5.2 Fractionation approaches to identify functional SOM
pools .................................................. 14
5.2.1 Hot water extractable С and N ................... 14
5.2.2 Particle size and density fractionation ......... 14
5.2.3 Soil microbial biomass .......................... 15
5.3 Soil enzyme activities ................................. 16
5.4 N mineralisation ....................................... 16
5.5 Decomposition experiments .............................. 16
5.6 Stable isotope analyses ................................ 17
5.7 Radiocarbon measurements ............................... 17
6 General Results and Discussion .............................. 17
6.1 Relationships between abiotic factors, the
composition of plant communities and the soil food
web (Chapter 1) ........................................ 18
6.2 Functional SOM pools: SOC stocks and stability
indicators (Chapter 2) ................................. 20
6.3 Bioavailability of ОС in functional SOM pools
(Chapter 3) ............................................ 22
7 Final Conclusions ........................................... 24
References ..................................................... 26
Chapter 1 Impact of the composition of the plant community
on labile soil organic carbon and soil food webs
in semi-natural grassland ecosystems of different
productivity
Abstract ....................................................... 34
Keywords ....................................................... 34
1 Introduction ................................................ 35
2 Materials and Methods ....................................... 37
2.1 Study area and plot description ........................ 37
2.2 Soil and vegetation analysis ........................... 37
2.3 Litter decomposition experiment ........................ 38
2.4 Hot water extractable С and N .......................... 38
2.5 Soil enzyme activities ................................. 39
2.6 PLFA analysis .......................................... 39
2.7 Data analysis .......................................... 40
3 Results ..................................................... 42
3.1 Decomposition of plant litter .......................... 42
3.2 Labile soil С and N fraction ........................... 42
3.3 Soil microbial properties .............................. 44
3.4 Relation between environmental factors and microbial
parameters ............................................. 45
4 Discussion .................................................. 46
4.1 The decomposability of plant litter and its effect on
labile soil С and N .................................... 46
4.2 Soil microbial components .............................. 48
4.3 Relation between environmental factors and microbial
parameters ............................................. 49
4.4 Conclusions ............................................ 50
Acknowledgments ................................................ 51
References ..................................................... 52
Supplementary Materials ........................................ 56
Chapter 2 Stability and stocks of organic carbon in
functional SOM pools through the soil profile of
semi-natural grassland ecosystems
Abstract ....................................................... 60
Keywords ....................................................... 60
1 Introduction ................................................ 61
2 Materials and Methods ....................................... 63
2.1 Site description ....................................... 63
2.2 Sampling ............................................... 63
2.3 Elemental analysis ..................................... 64
2.4 Calculation of С stocks and carbon enrichment
factors (ESOC) .......................................... 65
2.5 Size-density fractionation ............................. 65
2.6 Hot water extractable С and N .......................... 66
2.7 Isotope analyses ....................................... 66
2.8 Data analysis .......................................... 66
3 Results ..................................................... 67
3.1 SOC stocks ............................................. 67
3.2 Carbon enrichment factors (ESOC) ........................ 69
3.3 Factors influencing SOC stocks ......................... 69
3.4 Hot water extractability of ОС in functional SOM
pools (CHWE-fraction) ..................................... 70
3.5 13C isotopic abundance of functional SOM pools and
bulk soil related to the CHWE percentage from SOC ...... 70
4 Discussion .................................................. 71
4.1 SOC stocks and С enrichment factors (ESOC) .............. 71
4.2 Factors influencing SOC stocks ......................... 74
4.3 Stability of functional SOM pools ...................... 74
4.4 Conclusions ............................................ 76
Acknowledgments ................................................ 77
References ..................................................... 77
Supplementary Materials ........................................ 81
Chapter 3 Microbial utilisation of functional SOM pools in
grassland ecosystems
Abstract ....................................................... 84
Keywords ....................................................... 84
1 Introduction ................................................ 85
2 Materials and Methods ....................................... 86
2.1 Study sites ............................................ 86
2.2 Soil and vegetation analysis ........................... 87
2.3 Size-density fractionation ............................. 87
2.4 Utilisation of functional SOM pools .................... 88
2.5 Microbial community .................................... 90
2.6 Microbial activity ..................................... 90
2.7 Statistical analyses ................................... 91
3 Results ..................................................... 92
3.1 Decomposition of functional SOM pools .................. 92
3.2 Soil microbial properties .............................. 92
3.2.1 Start of the incubation experiment .............. 93
3.2.2 End of the incubation experiment ................ 93
3.2.3 Change of microbial properties during
utilisation of functional SOM pools ............. 95
4 Discussion .................................................. 97
4.1 Functional SOM pools isolated by particle size ......... 97
4.2 Functional SOM pools isolated by specific density ...... 99
4.3 Conclusions ........................................... 100
Acknowledgments ............................................... 101
References .................................................... 101
Supplementary Materials ....................................... 105
Acknowledgments ............................................... 110
Curriculum Vitae .............................................. 1ll
Declaration ................................................... 112
Erklärung ..................................................... 112
List of Publications .......................................... 113
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