Preface to Second Edition xiii
Preface to First Edition xv
1 Plants, Roots and the Soil 1
1.1 Evolution of Roots 2
1.2 Root and Shoot Coordination 6
1.2.1 Communication Between Roots and Shoots 6
1.2.2 Coordination of Growth 9
1.3 Roots and the Soil 11
1.3.1 Rootâ"Soil Interface 12
1.3.2 Rootâ"Induced Soil Processes 15
References 18
2 Roots and the Architecture of Root Systems 23
2.1 Nomenclature and Terminology 23
2.2 Root Anatomy 25
2.2.1 Primary Structure 26
2.2.2 Secondary Structure 32
2.3 Root Tip 36
2.3.1 Root Cap and Border Cells 36
2.3.2 Mucilage 39
2.4 Extension and Branching 42
2.4.1 Extension 42
2.4.2 Root Hairs 45
2.4.3 Branching 48
2.5 Adventitious and Specialised Roots 52
2.6 Architecture of Root Systems 57
References 62
3 Development and Growth of Root Systems 71
3.1 Measurement of Root Systems 71
3.1.1 Field Techniques 72
3.1.1.1 Extraction 72
3.1.1.2 Observation 74
3.1.1.3 Inference Techniques 78
3.1.2 Laboratory Techniques 78
3.1.3 Root Phenotyping 80
3.2 Root System Development and Phenology 82
3.3 Size and Distribution of Root Systems 84
3.3.1 Mass and Length 84
3.3.2 Depth of Rooting 91
3.3.3 Distribution of Roots 94
3.4 Root:Shoot Allocation of Dry Matter 96
3.5 Root Longevity and Turnover 97
3.6 Modelling of Root Systems 102
3.6.1 Depth and Distribution Models 102
3.6.2 Density-Based Diffusion Models 103
3.6.3 Root System Architectural Models 106
3.6.4 Crop Models 109
References 112
4 The Rhizosphere 123
4.1 Microbial Communities and Biochemical Changes 125
4.1.1 General Features 125
4.1.2 Nitrogen Availability 127
4.1.3 Phosphorus Availability 130
4.1.3.1 Root Hairs 131
4.1.3.2 Organic Anions 131
4.1.3.3 Enzymes 135
4.1.3.4 Arbuscular Mycorrhizal Fungi and the Hyphosphere 137
4.1.4 Availability of Other Nutrients 137
4.2 Rhizodeposition 139
4.2.1 Rhizodeposits â" Quantities and Composition 139
4.2.2 Root Exudates 143
4.2.3 Carbon Sequestration by Soil 146
4.2.4 Root Exudates and Phytosiderophores 148
4.3 Rhizosphere Signalling 150
4.3.1 Microbiome-Root-Shoot Signalling 151
4.3.2 Cross-Kingdom Signalling 151
4.3.3 Gaseous Signals 153
4.4 Chemical and Physical Changes in the Rhizosphere 153
4.4.1 Chemical Changes 154
4.4.1.1 Changes in pH 154
4.4.1.2 Changes in Redox (Eh) Conditions 156
4.4.2 Soil Structure in the Rhizosphere 159
4.4.3 Soil Water 161
4.4.4 Engineering and Managing the Rhizosphere 163
References 164
5 Roots and the Biological Environment 177
5.1 Interactions of Roots with Soil Organisms 177
5.1.1 Rootâ"Microbiome Signalling 177
5.1.2 Interactions with Bacteria 180
5.1.3 Interactions with Fungi 184
5.1.4 Interactions with Protozoa 185
5.1.5 Interactions with Meso-fauna 186
5.2 Endosymbiotic Associations 189
5.2.1 Mycorrhizas 190
5.2.2 Rhizobia and N Fixation 203
5.3 Root Pathogens and Parasitic Associations 209
5.3.1 Fungal Diseases 209
5.3.2 Nematodes 212
5.3.3 Parasitic Weeds 215
5.4 Root Herbivory by Insects 219
References 221
6 Roots and the Physico-Chemical Environment 233
6.1 Temperature 233
6.1.1 Root Development and Growth 235
6.1.2 Root Orientation and Root System Architecture 238
6.1.3 Extremes of Cold and Heat 239
6.2 Tropic Responses 240
6.2.1 Gravitropism 241
6.2.2 Hydrotropism, Hydropatterning and Xerobranching 243
6.2.3 Phototropism and Thigmotropism 246
6.3 Soil Chemical Environment 248
6.3.1 Plant Nutrients 248
6.3.2 Low pH and Aluminium 257
6.3.3 Salinity 260
6.4 Soil Mechanical Properties 261
6.4.1 Root Elongation and Mechanical Impedance 262
6.4.2 Root Responses to Mechanical Impedance 265
6.4.3 Roots and Soil Structure 270
6.5 Soil Pores and Their Contents 271
6.5.1 Soil Water 271
6.5.2 Soil Aeration and Waterlogging 275
6.6 Global Environmental Change 277
6.6.1 Atmospheric CO 2 Concentration 278
6.6.2 Global Warming 279
6.6.3 Precipitation 281
References 282
7 The Functioning Root System 295
7.1 Root Anchorage 295
7.1.1 Uprooting 296
7.1.2 Overturning 299
7.2 Nutrient Uptake 306
7.2.1 Nutrient Requirements of Plants and Their Availability in Soil 306
7.2.2 Nutrient Movement in Soil Solution 308
7.2.3 Solute Movement Across the Root 311
7.2.3.1 Transport Pathways 311
7.2.3.2 Endodermis, Casparian Strip and Suberin Lamellae 313
7.2.3.3 Nutrient Carriers 314
7.2.4 Solute Movement in the Stele 320
7.2.5 Nutrient Uptake by Root Systems 321
7.2.5.1 Root Ideotypes 321
7.2.5.2 Modelling Nutrient Uptake 323
7.3 Water Uptake 328
7.3.1 Soilâ"Plantâ"Atmosphere Continuum 329
7.3.1.1 Water Movement in Soil 331
7.3.1.2 Water Movement From Soil to Root 332
7.3.2 Water Movement Across the Root 334
7.3.2.1 Water Movement From Soil Layer to Soil Layer via Roots 335
7.3.3 Water Uptake by Root Systems 337
7.3.3.1 Modelling Water Uptake 339
References 342
8 Genetics and Breeding of Root Systems 351
8.1 Genotypic Differences in Root Traits 351
8.1.1 Root System Architecture and Anatomy 352
8.1.2 Functional Traits 355
8.1.2.1 Anchorage 355
8.1.2.2 Nutrient Acquisition 356
8.1.2.3 Water Acquisition 357
8.2 Mapping the Genetic Loci of Root Traits 359
8.2.1 Use of Mutants 361
8.2.2 Identification of Quantitative Trait Loci for Root Traits 364
8.3 Root Traits for Enhanced Nutrient Acquisition 370
8.3.1 Root Architecture and Anatomy 370
8.3.2 Root Hairs 372
8.3.3 Root-Released Enzymes 376
8.4 Root Traits for Drought 378
8.4.1 Deep Rooting 378
8.4.2 Root Anatomy 380
8.5 Breeding 382
8.5.1 Breeding Successes 382
8.5.2 Future Breeding 385
References 386
9 Root Systems as Management Tools 395
9.1 Optimal Root Systems and Competition for Resources 395
9.2 Intercropping and Agroforestry 398
9.3 Crop Rotations 406
9.3.1 Deep Rooting and Use of Subsoil Resources 406
9.3.2 Root Release of Secondary Metabolites: Allelopathy, Biofumigation and Replant Disease 413
9.4 Rootstocks 417
9.5 Exploiting Root Parasitism 420
9.6 Phytoremediation 422
9.7 Soil Stabilisation 424
References 426
Index 437
