Contributors ................................................... xi
Preface ...................................................... xiii
1 Water use efficiency in plant biology ......................... 1
MARK A. BACON
1.1 Introduction .............................................. 1
1.1.1 The global perspective .............................. 1
1.1.2 Definition of water use efficiency .................. 2
1.1.3 Historical perspective .............................. 2
1.2 Carbon metabolism and WUE ................................. 4
1.2.1 WUE and the regulation of assimilation .............. 4
1.2.2 Photosynthetic biochemistries and WUE ............... 4
1.2.3 Isotope discrimination and WUE ...................... 6
1.3 Stomata and WUE ........................................... 9
1.4 Leaf growth and WUE ...................................... 11
1.5 Roots, hydraulic conductivity and WUE .................... 12
1.6 Uncovering the genetic basis to WUE ...................... 15
1.7 Adaptations to drought and water use efficiency .......... 17
1.8 Phenology, the environment and agronomy .................. 18
1.9 Delivering enhanced WUE into agriculture and
horticulture ............................................. 19
1.9.1 Drysdale Wheat ..................................... 19
1.9.2 Partial rootzone drying ............................ 20
1.10 Summary ................................................. 22
References ................................................... 22
2 What is water use efficiency? ................................ 27
HAMLYN JONES
2.1 Introduction ............................................. 27
2.2 Drought tolerance and the importance of water use
efficiency ............................................... 27
2.3 Definitions of water use efficiency ...................... 29
2.3.1 Intrinsic water use efficiency ..................... 30
2.3.2 Instantaneous versus integral water use
efficiency ......................................... 31
2.4 Variability in WUE ....................................... 31
2.5 Gas exchange ............................................. 34
2.5.1 Plant-atmosphere coupling .......................... 35
2.5.2 Integration over time .............................. 36
2.6 Methodology .............................................. 37
2.7 Water use efficiency and productivity .................... 39
References ................................................... 40
3 Water use efficiency and photosynthesis ...................... 42
M.M. CHAVES, J. OSÓRIO and J.S. PEREIRA
3.1 Introduction ............................................. 42
3.2 The carbon compromise .................................... 43
3.3 Genetic and environmental constraints to A, gs, gw and
WUE ...................................................... 45
3.4 WUE in plants growing under elevated CO2 in the
atmosphere ............................................... 50
3.5 Trade-offs in resource use efficiencies - nitrogen,
radiation and water ...................................... 51
3.5.1 Trade-offs ......................................... 53
3.5.2 A case study ....................................... 57
3.6 Patterns of carbon to water balance in natural
vegetation ............................................... 60
3.6.1 Using isotope discrimination to study WUE .......... 60
3.6.2 Differences in WUE between plant functional
types .............................................. 62
3.6.3 WUE along environmental gradients .................. 64
References ................................................... 66
4 Water use efficiency and chemical signalling ................. 75
SALLY WILKINSON
4.1 Introduction ............................................. 75
4.1.1 Definitions ........................................ 75
4.1.2 Background to chemical signalling .................. 77
4.2 Abscisic acid and xylem sap pH as signals of soil water
and nutrient availability ................................ 80
4.2.1 Effects of ABA in plants ........................... 80
4.2.2 How the ABA/pH signal works ........................ 81
4.2.3 Evidence for the pH signal ......................... 85
4.2.4 pH as a signal controlling fruit growth ............ 87
4.2.5 pH as a signal of soil flooding .................... 88
4.2.6 Proposed mechanisms for the pH change .............. 90
4.2.7 ABA-conjugates ..................................... 93
4.3 Abscisic acid and xylem sap pH as signals of changes in
the aerial environment ................................... 94
4.4 Other chemical regulators (cytokinins, ethylene and
nitrate) ................................................. 98
4.4.1 ACC and ethylene ................................... 98
4.4.2 Nitrate ........................................... 102
4.4.3 Cytokinins ........................................ 103
4.5 Factors affecting stomatal responses to chemical
signals ................................................. 104
4.6 Conclusions ............................................. 107
References .................................................. 107
5 Physiological approaches to enhance water use efficiency
in agriculture: exploiting plant signalling in novel
irrigation practice ......................................... 113
B.R. LOVEYS, M. STOLL and W.J. DAVIES
5.1 Introduction ............................................ 113
5.2 Understanding the ways in which WUE can be influenced ... 115
5.2.1 Stomatal regulation of gas exchange ............... 115
5.2.2 Regulation of plant development and functioning ... 116
5.3 Regulated Deficit Irrigation (RDI) and Partial
Rootzone Drying (PRD) Irrigation ........................ 122
5.3.1 Regulated Deficit Irrigation ...................... 122
5.3.2 Partial Rootzone Drying ........................... 125
Acknowledgements ............................................ 138
References .................................................. 138
6 Agronomic approaches to increasing water use efficiency ..... 142
PETER J. GREGORY
6.1 Summary ................................................. 142
6.2 Introduction ............................................ 142
6.3 Agronomic definitions of water use efficiency ........... 143
6.4 Crop and genotype influences on transpiration
efficiency .............................................. 145
6.5 Management of water in rainfed crop production .......... 149
6.5.1 Increasing T relative to other losses ............. 151
6.5.2 Increasing the total water supply ................. 156
6.6 Management of water in irrigated crop production ........ 159
6.7 Interactions between soils, climate and crop
management .............................................. 161
6.8 WUE and trade-off issues in a wider context ............. 164
References .................................................. 167
7 Plant nutrition and water use efficiency .................... 171
JOHN A. RAVEN, LINDA L. HANDLEY and BERND WOLLENWEBER
7.1 Introduction ............................................ 171
7.2 Defining the status of nutrient elements used by
plants .................................................. 171
7.2.1 The nutrient elements ............................. 171
7.2.2 Sources on nutrient elements: spatial aspects ..... 173
7.2.3 Sources of nutrient elements: speciation .......... 173
7.2.4 Sources of nutrient elements: deficiency and
excess ............................................ 175
7.3 The observed effects on water use efficiency of
nutrient element deficiency and excess and variation
in nutrient element source .............................. 175
7.3.1 Methodological considerations ..................... 175
7.3.2 Observations ...................................... 176
7.4 Water use efficiency and nutrient availability to (and
content in) the plant: mechanistic considerations ....... 179
7.4.1 Does nutrient content relate to water use
efficiency via effects of water influx on solute
influx from the soil solution? .................... 179
7.4.2 Stomatal conductance .............................. 181
7.4.3 Biochemical capacity for photosynthesis ........... 182
7.4.4 Xylem conductance ................................. 183
7.4.5 Organic carbon loss ............................... 183
7.4.6 Inorganic carbon loss ............................. 184
7.5 The effect of interactions among organisms on
nutrition and on water use efficiency ................... 184
7.5.1 Symbioses ......................................... 184
7.5.2 Populations ....................................... 187
7.5.3 Communities ....................................... 187
7.5.4 Agriculture ....................................... 188
7.6 Conclusions ............................................. 189
Acknowledgements ............................................ 190
References .................................................. 190
8 Crop yield and water use efficiency: a case study in rice ... 198
JIANHUA ZHANG and JIANCHANG YANG
8.1 Water shortage in crop production: a growing crisis ..... 198
8.2 Water-saving cultivation of rice: problems and
possibilities ........................................... 199
8.3 A trade-off between grain yield and WUE? ................ 203
8.4 Grain filling: concurrent photosynthesis and
remobilization of pre-stored carbon ..................... 204
8.5 Problems in grain filling ............................... 205
8.6 Controlled soil drying to promote whole plant
senescence at grain filling ............................. 206
8.7 Plant hormones and key enzymes in the enhanced
remobilization of pre-stored reserve .................... 218
8.8 Conclusions ............................................. 222
Acknowledgement ............................................. 223
References .................................................. 223
9 Molecular approaches to unravel the genetic basis of water
use efficiency .............................................. 228
ROBERTO TUBEROSA
9.1 Introduction ............................................ 228
9.2 Target traits influencing WUE ........................... 229
9.2.1 Carbon isotope discrimination ..................... 231
9.2.2 Stomatal conductance .............................. 232
9.2.3 Canopy temperature ................................ 234
9.2.4 Abscisic acid ..................................... 234
9.2.5 Water potential and relative water content of
the leaf .......................................... 236
9.2.6 Osmotic adjustment ................................ 236
9.2.7 Root traits ....................................... 237
9.2.8 Early vigour and flowering time ................... 238
9.3 QTLs for WUE and related traits in crops ................ 240
9.3.1 The QTL approach: where genetics, crop
physiology and breeding meet ...................... 240
9.3.2 Case studies in dicots ............................ 244
9.3.3 Case studies in cereals ........................... 247
9.4 What can we learn through the 'omics' approach? ......... 256
9.4.1 Transcripome analysis ............................. 257
9.4.2 Proteomics and metabolomics ....................... 260
9.5 From QTLs to genes for WUE and related traits ........... 263
9.5.1 Positional cloning ................................ 264
9.5.2 The candidate gene approach ....................... 264
9.6 Conventional and molecular approaches to improve WUE
and drought tolerance ................................... 267
9.6.1 Empirical vs. analytical breeding ................. 268
9.6.2 Marker-assisted selection ......................... 269
9.6.3 Genetic engineering ............................... 273
9.7 Conclusions ............................................. 279
References .................................................. 282
10 Water use efficiency in the farmers' fields ................ 302
JOHN PASSIOURA
10.1 Introduction .......................................... 302
10.2 WUE on farm ........................................... 303
10.3 Accessing more of the water supply .................... 307
10.3.1 Canopy development to reduce evaporative
losses from the soil ........................... 307
10.3.2 Reducing losses of water by deep drainage ...... 310
10.4 Improving transpiration efficiency, the exchange of
water for CO2 ......................................... 312
10.5 Converting biomass into grain ......................... 313
10.5.1 Adapting phenology to environment .............. 313
10.5.2 Effects of drought on fertility ................ 315
10.5.3 Mobilising pre-anthesis reserves during
grain filling .................................. 316
10.6 The impact of spatial variability ..................... 317
10.7 Concluding comments ................................... 317
Acknowledgements ........................................... 318
References ................................................. 318
Index ......................................................... 322
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