Physiological Processes in Plant Ecology : Toward a Synthesis with Atriplex

In the spring of 1969 a small meeting was convened at the CSIRO Riverina Laboratory, Deniliquin, New South Wales, to discuss the biology of the genus Atriplex, a group of plants considered by those who attended to be of profound importance both in relation to range management in the region and as a tool in physiological research. The brief report of this meeting (Jones, 1970) now serves as a marker for the subsequent remarkable increase in research on this genus, and served then to interest the editors of the Ecological Studies Series in the present volume. This was an exciting time in plant physiology, particularly in the areas of ion absorption and photosynthesis, and unknowingly several laboratories were engaged in parallel studies of these processes using the genus Atriplex. It was also a time at which it seemed that numerical methods in plant ecology could be used to delineate significant processes in arid shrubland ecosystems. Nevertheless, to presume to illustrate and integrate plant physiology and ecology using examples from a single genus was to presume much. The deficiencies which became increasingly apparent during the preparation of the present book were responsible for much new research described in these pages.

1. Physiological Processes in Plant Ecology: the Structure for a Synthesis.- 1.1 The Space-Time Scale.- 1.2 Utility of the Space-Time Scale.- 1.3 The Quest for Adaptive Significance Among Physiological Processes.- 1.4 Structure for a Synthesis.- 2. Systematic and Geographical State of Atriplex.- 2.1 The Habit and Morphology of Atriplex.- 2.1.1 The Fruiting Bracts.- 2.1.2 Seed Morphology.- 2.1.3 Epidermal Trichomes.- 2.1.4 Leaf Morphology and Anatomy.- 2.2 A Species List for Atriplex.- 2.3 Geographical Distribution of Species.- 2.3.1 Diversification of Species in Relation to Aridity.- 2.3.2 The Tropics as Barriers to Migration.- 2.3.3 Origins of the Genus.- 2.4 Perspectives from the Systematic and Geographical States.- 3. Genecological Differentiation.- 3.1 Intra-Specific Variation and Ecotypic Differentiation.- 3.2 Morphological Aspects of Genecological Differentiation.- 3.3 Genetic Coherence Between Functional and Morphological Characteristics.- 3.4 Physiological Aspects of Genecological Differentiation.- 3.4.1 Light Intensity.- 3.4.2 Temperature.- 3.4.3 Drought.- 3.4.4 Edaphic Factors.- 3.5 Concluding Remarks.- 4. Genetic and Evolutionary Relationships in Atriplex.- 4.1 Chromosome Numbers in Atriplex.- 4.2 Genetic Structures and Evolutionary Trends in the Atriplex triangularis Group.- 4.2.1 Prezygotic Hybridization Barriers.- 4.2.2 Zygotic Hybridization Barriers.- 4.2.3 Polymorphism.- 4.2.4 Evolutionary Trends.- 4.3 Interspecific Relationships and Distribution of C4 Photosynthesis in Atriplex.- 4.3.1 C4 Photosynthesis.- 4.3.2 A Phylogenetic Scheme for Atriplex.- 4.3.3 Inter-Specific Crossing Experiments in Atriplex.- 4.3.4 Inter-Specific Hybridization in Natural Populations.- 4.3.5 DNA Sequence Comparisons in Atriplex.- 4.3.6 Intraspecific C3/C4 Differentiation?.- 4.4 Inheritance of C4 Photosynthesis in Atriplex.- 5. Atriplex Communities: Regional Environments and Their Ecological Analysis.- 5.1 Communities of Arid Continental Interiors.- 5.1.1 Arid Shrub Steppe.- 5.1.2 Arid Halophytic Communities.- 5.2 Coastal Communities.- 5.2.1 Sand Dune Communities.- 5.2.2 Salt Marsh Communities.- 5.3 Weed and Ruderal Communities.- 5.4 The Major Atriplex Habitats ― a Resumé.- 5.5 Regional Variation in Atriplex Shrublands.- 5.5.1 Ordination of Large-Scale Variation in Plant Communities.- 5.5.2 Ordination of the Australian Arid Shrublands.- 5.6 Local Variation and Pattern in Atriplex Shrublands.- 5.6.1 Pattern Analysis.- 5.6.2 Pattern Analysis in Arid Atriplex Shrublands.- 5.7 Regularity in Arid Vegetation.- 5.8 Patterns of Biomass and Nutrient Distribution.- 5.8.1 Biomass Distribution in Arid Shrublands.- 5.8.2 Nutrient and Salt Distribution.- 5.8.3 Distribution of Microbiological Activity.- 5.9 Ecological States in Perspective.- 6. Germination and Seedling Establishment.- 6.1 Germination Processes.- 6.1.1 Water Relations of Germinating Seeds.- 6.1.2 Fruit Morphology and the Soil to Seed Water Potential Gradient.- 6.1.3 Seed Dimorphism and the Conductance of the Water Transport Pathway.- 6.1.4 Temperature Responses of Germination.- 6.1.5 Germination and Light.- 6.1.6 Gas Exchange and Seed Germination.- 6.1.7 Other Factors Regulating Germination.- 6.2 Establishment Processes.- 6.2.1 Water Relations During Establishment.- 6.2.2 Nutrition During Establishment.- 6.2.3 Metabolic and Morphological Changes During Establishment.- 6.3 Physiological Processes of Germination and Establishment in the Context of Ecological Processes.- 6.3.1 Germination Processes and Reproductive Strategy.- 6.3.2 Dispersal Factors in Germination and Establishment.- 6.3.3 Herbivory in Germination and Establishment.- 6.3.4 Evaluation of Germination and Establishment Processes.- 6.3.5 Establishment Processes and Population Dynamics in Natural Conditions.- 6.4 Conclusions.- 7. Absorption of Ions and Nutrients.- 7.1 Ionic Concentration, Distribution, and Pathways in the Soil-Plant System.- 7.1.1 States of Ions and Nutrients in the Soil.- 7.1.2 Pathways and Compartments for Ions in Plants.- 7.1.3 States of Ions and Nutrients in Plants.- 7.2 Ion Absorption Processes in Plants.- 7.2.1 Ion Absorption and Concentration.- 7.2.2 Passive and Active Processes of Ion Absorption.- 7.3 Absorption of Nutrient Anions and Interactions with Cell Metabolism.- 7.3.1 Nitrogen Absorption and Incorporation.- 7.3.2 Metabolic Consequences of Nitrogen Incorporation.- 7.3.3 Interactions Between NO3? and Cl? During Absorption and Incorporation.- 7.3.4 Efficiency of Nitrogen Utilization.- 7.3.5 Phosphate Absorption.- 7.3.6 Micronutrient Ions and Toxicity.- 7.4 Salinity Responses in Atriplex.- 7.4.1 Salt Exclusion, Salt Accumulation, and Salinity Tolerance.- 7.4.2 Salt Absorption by Atriplex Seedlings as a Function of External Concentration.- 7.4.3 NaCl Uptake and Transport.- 7.4.1 K+ and Na+ Selectivity in Halophytes.- 7.4.2 Ion Uptake and Excretion in Leaves.- 7.4.3 Salinity, Metabolism and Growth.- 7.5 Ion and Nutrient Absorption Processes in the Context of Ecological Processes.- 7.5.1 Mineral Cycling Within the Plant Community.- 7.5.2 Mineral Cycling and Stability of Arid Shrublands.- 7.5.3 Consequences of Plant Ion and Nutrient Absorption Processes at Higher Trophic Levels.- 7.2 Conclusions.- 8. Water Movement and Plant Response to Water Stress.- 8.1 Water Transport.- 8.1.1 The States of Water.- 8.1.2 Water Potentials in the Atmosphere, Plant, and Soil.- 8.1.3 Pathways for Water Movement.- 8.1.4 Dynamics of Water Movement Through the Plant.- 8.1.5 Water Movement in Relation to Energy Balance.- 8.1.6 Components of Water Potential.- 8.2 Response and Adaptation to Water Stress.- 8.2.1 Stomatal Regulation of Water Loss and Water Use Efficiency.- 8.2.2 Changes in Leaf Inclination and Reflectance.- 8.2.3 Root Extension and Water Uptake.- 8.2.4 Osmotic Adjustment in Response to Low Tissue Water Potential.- 8.2.5 Conclusions.- 9. Photosynthesis.- 9.1 The Photosynthetic Process.- 9.1.1 Photochemistry.- 9.1.2 C02 Fixation and Metabolism.- 9.2 Photosynthetic Responses to Light.- 9.2.1 Photosynthetic Light Acclimation in Atriplex triangularis.- 9.2.2 Photoinhibition.- 9.2.3 Light Utilization by C3 and C4Atriplex spp.- 9.3 Photosynthetic Responses to Temperature.- 9.3.1 Photosynthetic Characteristics of Cold-Adapted and Heat-Adapted C3 and C4 Plants.- 9.3.2 Environmentally Induced Acclimation to Temperature.- 9.3.3 Leaf Factors Determining Photosynthetic Capacity at Low Temperatures.- 9.3.4 High Temperature Stability of Photosynthesis.- 9.4 Photosynthesis in Relation to Water Use and Water Stress.- 9.4.1 Photosynthetic Water Use Efficiency.- 9.4.2 Photosynthesis in Relation to Water Stress.- 9.5 Photosynthesis in Relation to Salinity and Mineral Nutrition.- 9.5.1 Response to Salinity.- 9.5.2 Response to Mineral Nutrition.- 9.5.3 Photosynthesis and Micronutrients.- 9.3 Conclusions.- 10. Productivity and Environment.- 10.1 Photosynthesis and Photosynthate Partitioning in Relation to Primary Productivity.- 10.2 Productivity in Relation to Light.- 10.3 Productivity in Relation to Temperature.- 10.3.1 Performance in Thermally Contrasting Habitats.- 10.3.2 Response of Growth to Temperature Under Controlled Conditions.- 10.3.3 Effect of Temperature on Photosynthate Partitioning.- 10.4 Productivity in Relation to Mineral Nutrition and Salinity.- 10.5 Productivity in Relation to Water.- 10.6 Productivity in Plant Communities.- 10.6.1 Annual Patterns of Productivity in Cool-Desert Shrub Communities.- 10.6.2 Long-Term Productivity in Arid Ecosystems.- 10.7 Effect of Future Increase in CO2 Level on Water Use and Productivity.- Epilog.- References.- Taxonomic Index.