1 Soil Factors Affecting Nutrient Bioavailability... 1 N.B. Comerford

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1 Contents 1 Soil Factors Affecting Nutrient Bioavailability N.B. Comerford 1.1 Introduction Release of Nutrients from the Soil Solid Phase Nutrient Movement Through the Soil Solution Nutrient Uptake by the Root System Modeling Nutrient Bioavailability Summary References Decomposition and Mineralization of Nutrients from Litter and Humus C.E. Prescott 2.1 Introduction Decomposition Early (Litter) Decomposition Moisture Temperature Litter Quality Nitrogen Availability Completeness of Decomposition Late-Stage Decomposition (Humus and Soil Organic Matter) Moisture Temperature Humus Quality Nitrogen Availability

2 X Contents Soil Texture Labile Carbon Nutrient Mineralization Summary References Integrated Root Responses to Variations in Nutrient Supply 43 D. Robinson 3.1 Introduction Spatial and Temporal Variations in Soil Nutrient Supplies Single Roots and Root Systems Local and Systemic Response Systems Local Responses Systemic Responses Emergent Integration Summary References Internal Regulation of Nutrient Uptake by Relative Growth Rate and Nutrient-Use Efficiency V.P. Gutschick, J.C. Pushnik 4.1 Introduction Phenomenology of Uptake Rate Responding to Nutrient-Use Efficiency and Growth Rate The Evolutionary and Ecological Perspective of Physiological Demand A View from Physiology: Response of Growth Rate to Nutrient Availability, Cost, and Utility Does a Simple Model Predict an Optimal Uptake Capacity and Root Allocation? Toward a Model of Uptake Regulation in Response to Nutrient Utility Predicted Response to an Intrinsic, Physiological or Developmental Limit on Relative Growth Rate Do Internal N and Carbohydrate Pools Explain Responses of V max to Photosynthetic N Utility and to Developmental Limitations on Relative Growth Rate?

3 Contents Applying the Model: Differences from Simple Functional Balance Additional Questions: Stress, Root Turnover, Low Set Points of Woody Plants Role of Root Lifetime Effects of Water Stress and Salinity Why Is Uptake so Low in Some Species? Conclusions Summary Appendix: Definitions of Terms and Symbols References XI 5 Biological Nitrogen Fixation Associated with Angiosperms in Terrestrial Ecosystems J.I. Sprent 5.1 Introduction Cyanobacteria and Their Symbioses Free-Living Nitrogen-Fixing Cyanobacteria Cyanobacterial Symbioses Cycads Gunnera Non-nodulating Associations Between Angiosperms and Non-photosynthetic Nitrogen-Fixing Microorganisms Loose Associations Endophytic Associations Kallar Grass Rice Sugarcane Nodulated Plants: Symbioses with Frankia and Rhizobia Actinorhizal Plants Parasponia Legumes Ecological Role and Uses of Nodulated Plants Actinorhizal Plants Legumes Nodulated and Non-nodulated Plants Geographical Trends Dry, Flooded and Saline Environments Possible Chemical Constraints Rhizobial Constraints

4 XII Contents Problems with Nodulated Legumes Mycorrhizas, Cluster (Proteoid) Roots and Other Nutrient Acquisition Systems How Much Nitrogen Is Fixed Biologically? What Does the Future Hold for Nitrogen-Fixing Plants? Summary References Homeostatic Processes for the Optimization of Nutrient Absorption: Physiology and Molecular Biology 117 A.D. Glass 6.1 Introduction Kinetic Constants for Ion Influx Definitions Methodology Effects of Nutrient Status on Kinetic Constants Natural Selection and Kinetic Constants High-Affinity and Low-Affinity Transporters From Black Box Kinetic Models of Regulation to Better Defined Mechanisms of Transport Regulation Molecular Basis of Nutrient Homeostasis Potassium Phosphate Sulfate Nitrogen Summary References Root Architecture and Nutrient Acquisition J. Lynch 7.1 Introduction Architectural Types Classes of Nutrient Resources Intrinsic and Extrinsic Roles of Root Architecture in Nutrient Acquisition Intrinsic Roles of Root Architecture in Nutrient Acquisition Efficiency of Vascular Networks

5 Contents XIII Dispersal of Root Foraging Structure of Root Demographics The Importance of Scale Extrinsic Roles of Root Architecture in Nutrient Acquisition Exploiting a Non-uniform Environment Interaction with Soil Organisms Competition Among Plants Practical Applications The Agroecology of Root Architecture Improving Crop Nutrient Efficiency Understanding and Managing Global Change Future Prospects Summary References The Efficiency of Nutrient Acquisition over the Life of a Root D.M. Eissenstat, A. Volder 8.1 Introduction Root Length and Absorptive Surface Area Importance Inconsistencies Between Root Length, Mycorrhizal Colonization and Observed Nutrient Uptake Root Architecture and Variation Among Fibrous Roots in a Single Root System Variation in Root Life Span in Different Environments and Among Species Costs of Root Production and Maintenance over a Root s Lifetime Biomass Costs of Producing Root Absorptive Surface Area Root:Shoot Biomass Partitioning Specific Root Length Root Hairs and Mycorrhizal Hyphae Costs of Root Respiration Construction Cost and Growth Respiration Maintenance Respiration Ion-Uptake Respiration Cost of Mycorrhizal Colonization and Maintenance Changes in C Costs as the Root Ages Other Costs

6 XIV Contents 8.4 Uptake of Mineral Nutrients over a Root s Lifetime Initial Advantages to Root Growth Importance of Mycorrhizal Colonization Longevity of Root Tissues Overview Longevity of Root Hairs and Epidermis Longevity of Cortex Longevity of Xylem Vessels Changes in Nutrient Uptake Capacity as the Root Ages The Efficiency of Nutrient Acquisition over a Root s Lifetime Efficiency Concepts and Model Simulations Problems Associated with Efficiency Efficiency Versus Effectiveness Problems of Currency Heterogeneous Soil Overview Effects of Water and Temperature Effects of Nutrient-Rich Patches Summary References Action and Interaction in the Mycorrhizal Hyphosphere a Reevaluation of the Role of Mycorrhizas in Nutrient Acquisition and Plant Ecology R. Finlay 9.1 Introduction Mycorrhizal Symbiosis and Its Quantitative Effects on Plant Nutrition Mycorrhizal Symbiosis an Overview Mycorrhizal Mycelia as Physical Extensions of Root Systems Qualitative Effects of Mycorrhizal Interactions with the Abiotic Environment Uptake and Utilisation of Organic Nutrients Weathering and Acquisition of Poorly Soluble Minerals Biotic Interactions Interactions with Bacteria Interactions with Fungi Interactions with Other Soil Organisms Multiplicity of Function Non-nutritional Roles Implications for Nutrient Cycling and Plant Ecology

7 Contents 9.7 Practical Implications of Mycorrhizosphere Effects Concluding Remarks Summary References XV 10 Effects of Soil Temperature on Nutrient Uptake K.S. Pregitzer, J.S. King 10.1 Introduction Dynamics of Soil Temperature The Soil Energy Balance Spatial and Temporal Variation in Soil Temperature Soil Temperature Effects on Soil Physical and Chemical Properties Soil Water Nutrient Transport Chemical Reactions Soil Temperature Effects on Root Biology Root Growth and Morphology Root Physiology Soil Temperature Effects on Soil Biology Decomposition and Nutrient Mineralization Soil Fauna Symbiotic Relationships Summary and Areas of Future Research References Nutrient Acquisition of Terrestrial Plants in a Changing Climate D.G. Bielenberg, H. BassiriRad Introduction Elevated Tropospheric Ozone or Elevated UV-B Radiation Extent of the Problem and Relevance to Nutrient Uptake Direct Effects on Nutrient Uptake Changes in Root-to-shoot Ratios, Morphology and Architecture Changes in Root Respiration and Carbohydrate Supply to the Roots

8 XVI Contents Changes in Root Uptake Kinetics Changes in Foliar Uptake/Leaching Indirect Effects on Nutrient Uptake Elevated Atmospheric CO 2 Concentration Extent of the Problem and Relevance to Nutrient Uptake Direct Effects of CO 2 on Plant Nutrient Uptake Changes in Root-to-Shoot Ratios Changes in Root Morphology and Architecture Changes in Root Uptake Kinetics Indirect Effects of CO 2 on Nutrient Availability at the Root Surface Summary References From Molecular Biology to Biogeochemistry: Toward an Integrated View of Plant Nutrient Uptake H. BassiriRad 12.1 Introduction Nutrient Bioavailability Plant Nutrient Demand and Use Efficiency Root System Traits That Regulate Nutrient Acquisition Global Change and Plant Nutrient Acquisition Broader Issues and Directions for Future Research References Subject Index

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