Methods of Studying Plant Water Relations

To write a handbook of methods is surely to invite criticism, as has already been said several times. On the other hand, there is a great need for methodological manuals in all fields of science. It was therefore decided to compile this book, written in good faith to help scientists, teachers and students who will, it is hoped, use it and judge it good. To be useful to the reader, such a manual must provide a broad review of the methods available and describe them in sufficient detail to permit preliminary selection and judgement. It has to give - at least for selected methods - a suffi­ ciently detailed description of the equipment and procedure as to be to some extent self-contained. It must assume a critical standpoint as regards the theoretical basis of the methods, the significance of results, and their errors and limitations. It must also furnish examples, pertinent numerical tables, and very complete references. All this and much more is expected of a good manual of methods.

1 Water in Cells and Tissues.- 1.1 Introduction and Terminology.- 1.2 Units of Water Potential and Examples of Absolute Values of Water Potential and its Components.- 1.3 The Determination of Water Potential (?w) of Cells and Tissues.- 1.3.1 Introduction.- 1.3.2 Compensation Methods in the Liquid Phase.- 1.3.2.1 Test Solutions.- 1.3.2.2 Cell and Segment Methods.- 1.3.2.3 Refractometric and Smear (Shardakov) Methods.- 1.3.2.4 Potometric (Volumetric) Method.- 1.3.3 Compensation Methods in the Gaseous Phase.- 1.3.3.1 Gravimetric Method.- Water Bath.- Measuring Vessels and Solutions.- Samples of Leaf Tissue, Weight Determination, Exposure and Evaluation of Results.- 1.3.3.2 Capillary Method.- 1.3.4 Psychrometric Methods.- 1.3.4.1 Principal Types of Psychrometers.- 1.3.4.2 Constant-temperature Water Bath.- 1.3.4.3 Construction of Psychrometers.- Type A (Peltier Psychrometer).- Type B (Droplet or Wet-loop Psychrometer).- Type C (Thermistor Psychrometer).- 1.3.4.4 Measuring Chambers and Arrangement of Samples.- 1.3.4.5 Measuring Procedures.- Meters for Measuring Thermocouple Output.- Measurement with Psychrometers of the A Type.- Measurement with Psychrometers of the B Type.- Isopiestic Technique.- Measurement with a Thermistor Psychrometer.- 1.3.4.6 Calibration.- 1.3.4.7 Psychrometric Measurements of the Water Potential of Intact Plants.- 1.3.4.8 Accuracy, Sources of Error, and Comparison of Psychrometric Methods.- 1.3.5 Dew-point Thermocouple Hygrometry.- 1.3.6 Volumetric Tensometric Method (Hanging Drop Method).- 1.3.7 Pressure Chamber Method.- 1.3.8 Determination of Freezing Point of Tissues.- 1.4 Determination of Osmotic Potential.- 1.4.1 Cell Methods.- 1.4.1.1 Method of Limiting Plasmolysis.- 1.4.1.2 Plasmometric Method.- 1.4.1.3 Zero Turgor Methods.- 1.4.1.4 Visual Melting Point Method.- 1.4.2 Methods Used for Determination of the Osmotic Potential of Expressed Cell Sap.- 1.4.2.1 Preparation of Cell Sap.- 1.4.2.2 Cryoscopy.- 1.4.2.3 Tensiometric Methods.- 1.4.2.4 Psychrometric Methods.- 1.4.2.5 Refractometric Method.- 1.4.3 Deformation Method for Measuring Osmotic Potential of Tissues.- 1.5 Determination of Turgor Pressure (Pressure Potential).- 1.5.1 Introduction.- 1.5.2 Calculations of Pressure Potential.- 1.5.3 Direct Measurements of Pressure Potential.- 1.5.4 Indirect Methods for Determination of Pressure Potential.- 1.6 Matric Potential, “Bound”, “Free” and “Mobile” Water.- 1.6.1 Introduction.- 1.6.2 Determination of Matric Potential.- 1.6.3 Determinations of “Free” and “Bound” Water.- 1.6.3.1 Dilatometric Method.- 1.6.3.2 Refractometric Method.- 1.6.3.3 Cryoscopic Method.- 1.6.3.4 Cobalt Chloride Method.- 1.6.4 Determination of “Mobile” Water.- 2 Water Content.- 2.1 Direct Methods of Water Content.- 2.1.1 Determination of the Water Content by Drying.- 2.1.2 Chemical Determination of Water by Titration.- 2.1.3 Other Methods.- Determination of Water in Microscopic Sections.- Determination of Water by Distillation with Toluene.- 2.2 Indirect Methods of Water Content.- 2.2.1 Measurement of the Absorption of Radioactive Radiation.- Determination of the Water Content of Leaves.- Determination of the Water Content of Thicker and Denser Organs.- Determination of the Water Content of a Plant Community.- 2.2.2 Measurement of Dielectric Constant (Capacitance) and Related Procedures.- 2.2.3 Measurement of Electrical Conductivity of the Tissue.- 2.2.4 Other Methods.- 2.3 Determination of the Water Content of Cell.- 2.4 Root Bridge Method.- 2.5 Water Saturation Deficit (Relative Water Content.- 2.5.1 Characteristics of These and Analogous Terms.- 2.5.2 Review and Discussion of the Methods which Have Been Used.- 2.5.3 Practical Hints.- 2.5.4 Determination of Harmful Water Saturation.- 2.5.4.1 Basic Terms.- 2.5.4.2 Techniques.- 3 Water Exchange between Plant Roots and Soil.- 3.1 Availability of Soil Water.- 3.1.1 Introduction.- 3.1.1.1 Static Availability of Soil Water.- 3.1.1.2 Dynamic Availability of Soil Water.- 3.1.2 Brief Review of Methods Used to Determine the Soil Water Content.- 3.1.3 Determination of Static Availability of Soil Water.- 3.1.3.1. Determination of Soil Water Potential.- 3.1.3.2 Determination of Matric Potential of Soil.- Soil Tensiometers.- Osmotic Tensiometer.- Resistance Block Method.- Other Methods for Matric Potential Estimation.- Suction Plate and Pressure Membrane.- 3.1.3.3 Determination of the Osmotic Potential of Soil Solution.- 3.1.4 Estimation of Dynamic Availability of Soil Water.- 3.1.4.1 Permanent Wilting Percentage.- Techniques Used to Determine P.W.P.- Examples of Standardized Procedures Used by Different Authors.- 3.1.5 Experimental Control of Soil Moisture.- 3.2 Determination of the Water Potential of.- 3.3 Determination of Water Absorption by.- 3.3.1 Potometric Determination of Rate of Water Absorption by a Complete Root System.- 3.3.2 Micropotometric Determination of the Differences in the Rate of Water Absorption in the Various Parts of a Single Root.- 3.3.3 Potometric Measurement of Experimentally Induced Water Uptake.- 3.3.4 Potometric Determination of Water Balance.- 3.3.5 Soil Potometers.- 3.4 Xylem Sap Exudation from Excised Roots and Root Systems.- 3.4.1 Introduction.- 3.4.2 Measurement of Sap Volume.- 3.4.3 Other Experimental Techniques.- 3.4.4 Determination of Root Pressure.- 3.4.5 Mathematical Models of Sap Exudation.- 4 Liquid Water Movement in Plants.- 4.1 Determination of Hydraulic Conductivity (Water Permeability) of Cytoplasm, Cell Membrane and Parenchymatous Tissues.- 4.1.1 “Osmotic” Measurements.- 4.1.2 “Pressure” Measurements.- 4.1.3 “Diffusion” Measurements.- 4.2 Measurements of the Velocity of Water Movement in Xylem.- 4.2.1 Heat Pulse Methods.- Measuring Procedures.- Heating Devices.- Temperature Sensing Elements.- 4.2.2 Radioactive Tracer Method.- 4.2.3 Magnetohydrodynamic Method.- 4.3 Measurements of the Volume Flux of Water in Xylem Vessels.- 4.3.1 Heat Balance Methods.- 4.3.2 Radioactive Tracer Methods.- 5 Water Exchange between Plant and Atmosphere.- 5.1 Introduction.- 5.2 Air Humidity.- 5.2.1 Expressions for Air Humidity and a Review of Methods Used for its Determination.- 5.2.2 Control of Air Humidity.- 5.3 Water Absorption by Aerial Parts of Plants.- 5.3.1 Introduction.- 5.3.2 Review of Methods Used to Measure Dew.- 5.3.3 Determination of Water Absorption by Aerial Parts.- 5.4 Ecological Factors in Transpiration.- 5.4.1 Evaporimeters. Equivalent Evaporation Power.- 5.4.2 Relative Transpiration.- 5.5 Transpiration.- 5.5.1 Introduction.- 5.5.2 Measurement of Instantaneous Transpiration Rate.- 5.5.2.1 Method of Short-term Weighing of Detached Parts of Plants.- 5.5.2.2 Short-term Gasometric Measurements.- 5.5.3 Continuous Measurement of the Transpiration Rate of Intact Plants.- 5.5.3.1 Gasometric Methods.- Gasometric Systems.- Transpiration Chambers.- Other Components of Gasometric Systems.- Infrared Analysers.- Psychrometric Methods.- Lithium Chloride and Other Resistance Hygrometers.- Dew-point Hygrometers.- Corona Hygrometer.- Microwave Hygrometer.- List of Manufacturers of Different Commercial Types of Hygrometers.- Thermoflux.- Gravimetric Absorption Methods.- 5.5.3.2 Gravimetric Methods.- 5.5.4 Measurement of Integrated Transpiration.- 5.5.5 Water Loss by Detached Leaves.- 5.5.6 Determination of Transpiration Resistance.- 5.5.6.1 Introduction.- 5.5.6.2 Calculation of Transpiration Resistances from Measurements of Steady State Transpiration Rate.- 5.5.6.3 Calculation of Transpiration Resistance from Leaf Energy Balance.- 5.5.6.4 Cobalt Chloride Paper Method.- 5.5.7 Transpiration Ratio and Productivity of Transpiration.- 5.5.8 Calculations of the Transpiration Rate and Examples.- 5.6 Stomata.- 5.6.1 Introduction.- 5.6.2 Frequency, Size and Shape of Stomata.- 5.6.3 Measurement of Stomatal Aperture.- 5.6.3.1 Direct Observation.- 5.6.3.2 Microrelief (Replica) Methods.- 5.6.3.3 Infiltration Methods.- 5.6.4 Porometry.- 5.6.4.1 Water Vapour Diffusion Porometers.- Unventilated Porometers.- Calibration of Unventilated Porometers.- Ventilated Porometers.- Calibration of Ventilated Porometers.- Steady State Diffusion Porometers.- 5.6.4.2 Diffusion Porometers Using Other Gases.- 5.6.4.3 Mass Flow Porometers.- Flow Rate Porometers.- Resistance Porometers.- Pressure - drop Porometers.- 5.7 Guttation.- 6 Table Appendix.- 6.1 Pertinent Physical Values, their Symbols and Units.- 6.2 Prefixes for Units.- 6.3 Some Mathematical Symbols.- 6.4 Some Physical Properties of Liquid Water.- 6.5 Some Physical Properties of Water Vapour.- 6.6 Absolute Air Humidity at Various Relative Air Humidities and Air Temperatures [Range -10 to 40°C and 10 to 100% r. h.].- 6.7 Absolute Air Humidity at Various Relative Air Humidities and Air Temperatures [Detailed Tables, Range 15 to 30°C and 40 to 100% r.h.].- 7 References.- Author Index.