This book provides an excellent illustration of the interrelationship between progress in scientific methodology and conceptual advances, and its publica­ tion should contribute to further advances. It is well known that major advances in understanding often follow the development of new methods. The development of the acetylene reduction assay for nitrogenase activity provides a good example of this interrelationship between theory and methods. Theoretical knowledge led to a search for substrates for nitro­ genase that could be assayed for more easily than ammonium, the normal product of the enzyme. The discovery of the reduction of acetylene to ethylene by nitrogenase provided the ideal answer to the problem by provid­ ing a rapid, specific, nondestructive, and inexpensive assay for nitrogenase activity. This assay is now used by almost every laboratory doing research on nitrogen fixation. However, further use and development of the acetylene reduction assay has shown that it can underestimate nitrogenase activity and can even give incorrect relative values under some circumstances. The major problem is that exposure of legume nodules to acetylene can cause a large increase in the resistance to oxygen diffusion into the nodule. This reduced supply of oxygen decreases the rate of nitrogenase activity within a few minutes.

Table of Contents:
1. A Multichannel System for Steady-State and Continuous Measurements of Gas Exchanges from Legume Roots and Nodules.- 1. Introduction.- 2. Overview of the Gas Exchange System.- 3. Application of the Gas Exchange System to Studies of Legume Physiology.- 4. Conclusions.- 2. Quantification of Diffusion Characteristics in Spherical Nodules: A Comparison of Methods.- 1. Introduction.- 2. Homogeneous Model of Nodule Diffusion.- 3. Diffusion Barrier Models.- 4. Comparisons Among Diffusion Barrier Models.- 5. Conclusions.- 6. Appendix. Sensitivity of Transient Analysis to Changes in Vmx.- 3. Simple Apparatus for Growth of Nodulated Plants and for Continuous Nitrogenase Assay Under Defined Gas Phase.- 1. Introduction.- 2. Apparatus — Plant Growth in Defined O2 Levels.- 3. Apparatus — Assays in Open, Flow-Through Systems.- 4. Continuous Measurements of Nitrogenase Activity in the Study of Environmental Responses of Frankia and Other Bacteria.- 1. Introduction.- 2. Materials and Methods.- 3. Results.- 4. Discussion.- 5. Limitations and Errors in Gas Exchange Measurements with Legume Nodules.- 1. Introduction.- 2. Sources of Error.- 3. Avoidance of the Acetylene-Induced Decline.- 4. Conclusions.- 6. Principles and Approaches in Modeling Steady-State Gas Diffusion in Legume Nodules.- 1. Introduction.- 2. General Diffusion Models.- 3. A Model of Gas Diffusion in Legume Nodules.- 4. Other Models of Gas Diffusion.- 7. Modeling Gas Exchange by Actinorhizal Root Nodules Using Network Simulation Analysis.- 1. Introduction.- 2. Model Construction.- 3. Simulation Model Output.- 4. Conclusions.- 8. Continuous and Steady-State Nutrient Absorption by Intact Plants.- 1. Introduction.- 2. Nutrient Flow System.- 3. Ion-Selective Electrodes.- 4. Measurement Artifacts.- 5. Validity ofContinuous and Steady-State Measurements.- 9. Steady-State Control and Investigation of Root System Morphology.- 1. Introduction.- 2. Overview.- 3. Environmental Factors which Affect Roots.- 4. Aeroponics.- 5. Conclusion.- 10. Measurement of Carbon Cost in Ectomycorrhizae.- 1. Introduction.- 2. Carbon Cost as Loss of Potential Dry Matter.- 3. Carbon Flow from Shoot to Root.- 4. Carbon Flow from Root to Fungus.- 5. Modeling Carbon Flow in Ectomycorrhizae.- 6. Conclusions.- 11. Approaches to Measuring Soil Nitrogen Transformations Under Continuous or Steady-State Conditions.- 1. Introduction.- 2. The Soil Environment.- 3. Soil Nitrogen Transformations.- 4. Continuous and Steady-State Terminology.- 5. Laboratory Methods.- 6. Field Methods.- 7. Isotope Dilution.- 8. Summary.- 12. Methodological Considerations in Measuring Biomass, Production, Respiration and Nutrient Resorption for Tree Roots in Natural Ecosystems.- 1. Introduction.- 2. Problems Associated with Field Root Studies.- 3. Root Biomass and Production.- 4. Root Respiration.- 5. Root Resorption of Nutrients.- 6. Conclusions.- Authors’ Index.