XI | P a g e
Table of content
REMERCIEMENTS ... V ABSTRACT ... VII RÉSUMÉ ... IX TABLE OF FIGURES ... XVII LIST OF TABLES ... XXV LIST OF ABBREVIATIONS ... XXVII
CHAPTER I – INTRODUCTION ... 1
1 CLAW HYPOTHESIS AND ITS POTENTIAL CLIMATE REGULATION ... 3
2 THE SULFUR CYCLE ... 9
2.1 ATMOSPHERE ... 9
2.2 LITHOSPHERE –HYDROSPHERE –BIOSPHERE ... 12
3 THE BIOGEOCHEMICAL CYCLE OF DMS ... 13
3.1 DMSP AND CH4 ... 14
3.2 THE BACTERIA AND ALGAL BIOSYNTHESIS OF DMS(P,O) ... 15
3.3 THE PHYSIOLOGICAL ROLES OF DMS(P,O) ... 18
3.3.1 Osmoprotectant ... 19 3.3.2 Cryoprotectant ... 20 3.3.3 Antigrazing compound ... 20 3.3.4 Infochemical ... 21 3.3.5 Overflow mechanisms ... 21 3.3.6 Antioxidant ... 21 4 THE FATE OF DMS(P,O) ... 22
4.1 THE FATE OF DMS(P,O) IN A MARINE ENVIRONMENT ... 22
4.2 THE FATE OF DMS ... 26
XII | P a g e
5.1 ROS PRODUCTION ... 30
5.2 HIGH LIGHT FORCING ... 31
5.3 CASCADE CHAIN REACTION WITH DMS(P,O) ... 34
5.4 PHYSIOLOGICAL IMPACT OF ROS FORMATION ... 39
6 STUDY CASES FOR BATCH MONOCULTURE ... 40
6.1 DIATOMS -SKELETONEMA COSTATUM ... 40
6.2 PRYMNESIOPHYCEAE -PHAEOCYSTIS GLOBOSA ... 42
6.3 DINOFLAGELLATES -HETEROCAPSA TRIQUETRA ... 44
7 STUDY CASES FOR FIELD SAMPLING... 47
7.1 THE NORTH SEA ... 47
7.2 THE PARTICULAR CASE OF THE BELGIAN COASTAL ZONE ... 48
8 RESEARCH OBJECTIVES ... 51
CHAPTER II – MATERIAL AND METHODS: OVERVIEW ... 53
1 PHYTOPLANKTON CULTURE ... 55 CULTURE EQUIPMENT ... 55 1.1 EXPERIMENTAL SETUP ... 55 1.2 SAMPLING ... 56 1.3 ANALYSES ... 57 1.3.1 Cell density... 57 1.3.2 Chlorophyll-a ... 57 1.3.3 DMS(P,O) ... 57 1.3.4 Chlorophyll fluorescence ... 57
1.3.5 Reactive Oxygen Species concentration ... 59
1.3.6 Lipid Peroxidation ... 59
2 FIELD SAMPLING ... 59
2.1 BELGIAN COASTAL ZONE ... 59
2.1.1 Sampling ... 59
2.1.2 DNA sequencing... 60
2.2 NORTHERN NORTH SEA ... 60
2.2.1 Sampling ... 60
XIII | P a g e CHAPTER III – RESPONSE OF DMSP AND DMSO CELL QUOTAS TO OXIDATIVE STRESS IN THREE
PHYTOPLANKTON SPECIES ... 61
1 ABSTRACT ... 63
2 INTRODUCTION ... 64
3 MATERIAL AND METHODS ... 66
3.1 ALGAL SPECIES AND CULTURE CONDITIONS... 66
3.2 EXPERIMENTAL TREATMENTS ... 66
3.3 ANALYSES ... 67
3.3.1 Carbon concentration ... 67
3.3.2 Chlorophyll concentrations ... 68
3.3.3 Chlorophyll fluorescence measurements ... 68
3.3.4 ROS production ... 69
3.3.5 Lipid peroxidation assay ... 70
3.3.6 DMS(P,O) analysis ... 70
3.4 STATISTICS ... 71
4 RESULTS ... 71
4.1 HIGH LIGHT STRESS ... 71
4.2 DCMU TREATMENT ... 74
4.3 MSB TREATMENT ... 74
4.4 PCA ... 75
5 DISCUSSION ... 78
5.1 DMS(P,O)P CONTENTS VARY AMONG PHYTOPLANKTON SPECIES INVESTIGATED. ... 79
5.2 DMS(P,O) ACT AS ANTIOXIDANT COMPOUNDS. ... 80
5.3 SPECIES ECOLOGICAL CHARACTERISTICS EXPLAIN THE EXPERIMENTAL RESULTS. ... 82
6 CONCLUSIONS ... 84
7 ACKNOWLEDGMENTS ... 84
8 APPENDIX ... 85
CHAPTER IV – DRIVERS OF THE VARIABILITY OF DMSP AND DMSO IN THE SOUTHERN NORTH SEA 89 1 ABSTRACT ... 91
2 INTRODUCTION ... 92
3 MATERIAL AND METHODS ... 94
XIV | P a g e
3.2 CHLOROPHYLL-A ... 95
3.3 PHYTOPLANKTON DIVERSITY ... 95
3.4 DMS(P,O) ANALYSIS ... 95
3.5 STATISTICAL ANALYSIS ... 97
4 RESULTS AND DISCUSSION ... 97
4.1 SPRING PHYTOPLANKTON BLOOM ... 98
4.2 SUMMER PHYTOPLANKTON BLOOM ... 102
4.3 SPATIAL AND SEASONAL VARIATIONS OF DMS(P,O) CONCENTRATIONS ... 103
4.4 DMS(P,O) RELATIONS AND DMSOP:DMSPP RATIO ... 107
4.5 PHYTOPLANKTON DIVERSITY AND DMS(P,O) ESTIMATION ... 111
5 CONCLUSIONS ... 111
6 ACKNOWLEDGEMENTS ... 113
CHAPTER V – DMSP AND DMSO VARIABILITY ALONG LATITUDINAL TRANSECTS AND DEPTHS IN THE NORTH SEA. ... 115
1 INTRODUCTION ... 117
2 MATERIAL AND METHODS ... 119
2.1 FIELD SAMPLING AND ABIOTIC PARAMETERS ... 119
2.2 BIOTIC PARAMETERS ANALYSIS ... 120
3 RESULTS AND DISCUSSION ... 121
3.1 THE ABIOTIC PARAMETERS AND THE CHL-A CONCENTRATIONS. ... 121
3.2 THE DMS(P,O)P PROFILES FOLLOWED THE CHL-A CONCENTRATIONS. ... 123
3.3 ANTIOXIDANT FUNCTION FOR DMS(P,O)P ... 128
3.4 DMS(P,O) PRODUCTION RESULTED FROM A MIXED PHYTOPLANKTON COMMUNITY. ... 132
3.5 DMS(P,O) ESTIMATIONS ... 133
4 CONCLUSIONS ... 136
5 ACKNOWLEDGEMENTS ... 136
6 APPENDIX ... 137
CHAPTER VI – DISCUSSION AND PERSPECTIVES ... 141
1 DISCUSSION AND PERSPECTIVES ... 143
1.1 ANTIOXIDANT FUNCTION ... 143
XV | P a g e
1.3 LIMITS AND PERSPECTIVES ... 148
1.3.1 Issues on the experimental design ... 149
1.3.2 Improvements of the experimental design ... 149
1.4 CELLULAR LOCATION, ISOTOPIC MEASUREMENTS, AND MOLECULAR TOOLBOX ... 150
2 CONCLUSIONS ... 152
