Between 1958 and 2008, the CO₂ concentration in the atmosphere increased from 316 to 385 ppm. Continued increases in CO₂ concentration will significantly affect long-term climate change, including variations in agricultural yields. Focusing on this critical issue, Elevated Carbon Dioxide: Impacts on Soil and Plant Water Relations presents research conducted on field-grown sorghum, winter wheat, and rangeland plants under elevated CO₂. It describes specific results from pioneering experiments performed over a seven-year period in the Evapotranspiration Laboratory at Kansas State University, along with experiments appearing in peer-reviewed journal articles.

Select articles from the literature serve as examples in the text. For each paper discussed, the author includes the common and scientific name of the plant under investigation. For each experiment, the author provides the type of soil used (if given in the original article) and general conditions of the experiment. All references are carefully documented so that readers can easily find the original source.

The first chapter of the book deals with drought, the three types of photosynthesis, and how water moves through the soil¿plant¿atmosphere continuum. With a focus on soil, the next several chapters discuss the composition of the soil atmosphere, the interaction of elevated CO₂ with physical factors that affect root growth, variable oxygen concentration of soil, and when the atmosphere above soil is elevated with CO₂.

The author goes on to examine the use of carbon isotope ratios in plant science; the effects of elevated CO₂ on plant water, osmotic, and turgor potentials; and stomata under elevated CO₂, including stomatal conductance and density. The text also explains the effects of elevated CO₂ on transpiration and evapotranspiration, explores historical aspects of water use efficiency, compares C₃ and C₄ plants under elevated CO₂, and details the advantages of C₄ photosynthesis. The concluding chapters cover plant anatomy, the effects of elevated CO₂ on phenology, and measures of plant growth.

How have plants responded to increased levels of atmospheric CO₂? Are some plants reacting better than others? Drawing on a host of scientific studies, this text explores how rising levels of CO₂ in the atmosphere have impacted water in plants and soils.

Elevated Atmospheric Carbon Dioxide: Drought
Introduction
Predictions
Photosynthesis of C₃ and C₄ Plants
Photosynthesis of CAM Plants
Field Studies with Crops
Controlled Environment Studies with Crops
Trees
Gymnosperm versus Angiosperm Trees
CAM Plant
Salinity

Elevated Carbon Dioxide in the Soil: Composition of the Soil Atmosphere
Introduction
Composition of the Soil Atmosphere
Organic Matter
Rainfall, Irrigation, and Flooding

Elevated Carbon Dioxide in the Soil: Interaction with the Soil Physical Factors That Affect Root Growth
Introduction
Soil Water
Soil Compaction
Soil Temperature

Elevated Carbon Dioxide in the Soil: Variable Oxygen Concentration and Root Growth
Introduction
Variable Oxygen Concentration in the Soil
Variation in Species
Soil versus Root Evolution of CO₂
Limiting Concentration of Oxygen
Maximum CO₂ in Soil That Allows Crop Growth
Movement of Gases Up and Down a Plant

Elevated Carbon Dioxide in the Atmosphere: Interaction with the Soil Physical Factors That Affect Root Growth
Introduction
Soil Water
Soil Compaction
Soil Temperature

Elevated Atmospheric Carbon Dioxide: Root Growth
Introduction
Field Studies with Sorghum and Wheat
Controlled-Environment Studies with Wheat
Soybeans, Tepary Bean, Bush Bean, Barley, and Cotton
Horticultural Crops
Pasture Plants
Native Grasses
Carbon Isotope Ratios of Plants with Different Photosynthetic Pathways
Trees
C₃ and C₄ Crops Compared
CAM Plants
Root-to-Shoot Ratios
Root Restriction

Elevated Atmospheric Carbon Dioxide: Plant Water Potential, Osmotic Potential, and Turgor Potential
Introduction
Wheat
Grassland Plants
Soybeans
Peas
Trees
Stress Relaxation
Native Herbs

Elevated Atmospheric Carbon Dioxide: Stomatal Conductance
Introduction
Leaf Resistances
Units
Factors That Control Stomatal Movements
Stomatal Conductance and Elevated CO₂
C₃ and C₄ Plants Compared

Elevated Atmospheric Carbon Dioxide: Stomatal Density
Introduction
Woodward¿s 1987 Discovery: Stomatal Density Decreases with Increasing CO₂ Concentration
Importance of Herbariums to Study the Historical Record of Stomata
Confirmation of the 1987 Discovery
Contradictions to the 1987 Discovery: No Effect of Elevated CO₂ on Stomatal Density
Brown and Escombe¿s Diameter Law
Amphistomatous and Hypostomatous Leaves
Sensitivity of Stomata to CO₂
Studies since Woodward¿s 1987 Discovery
Studies of Fossil Plants
Stomatal Anatomy and Elevated CO₂
How Does Stomatal Density Change with CO₂ Concentration?

Elevated Atmospheric Carbon Dioxide: Transpiration and Evapotranspiration
Introduction
Transpiration under Greenhouse Conditions
Carbon Dioxide Enrichment in Greenhouses
Ethylene
Transpiration under Elevated CO₂
Evapotranspiration¿General Principles
Evapotranspiration under Elevated CO₂

Elevated Atmospheric Carbon Dioxide: Water Use Efficiency
Introduction
Definitions and Historical Aspects of Efficient Water Use
Water Requirement of C₃ and C₄ Plants
Water Use Efficiency under Elevated CO₂
Water Use Efficiency of Fossil and Herbarium Plants

Elevated Atmospheric Carbon Dioxide: C₃ and C₄ Plants
Introduction
C₃ versus C₄ Photosynthesis
Advantage of C₄ Photosynthesis
Dry Matter Production of C₃ and C₄ Plants
Evolution of C₄ Plants
C₃ and C₄ Plants under Elevated CO₂

Elevated Atmospheric Carbon Dioxide: Plant Anatomy
Introduction
Leaves
Comparison of C₃ and C₄ Leaves
Leaf Ultrastructure
Wood Anatomy and Density under Variable CO₂ Concentrations
Wood Anatomy under Variable Precipitation and Ambient CO₂
Internal Leaf Characteristics of C₃ and C₄ Plants under Ambient CO₂

Elevated Atmospheric Carbon Dioxide: Phenology
Introduction
Phenology
Wheat Physiology and Phenology
Methods to Determine Crop Development
Q ₁₀, Degree-Day Concept and Heat Units
Growth Stages of Wheat as Affected by Elevated CO₂
Phenology under Elevated CO₂
Questions to Be Answered about Elevated CO₂ and Phenology

Elevated Atmospheric Carbon Dioxide: Growth and Yield
Introduction
Wheat
Rice
Barley
Oats
Soybean
Cotton
Horticultural Crops
Pasture and Grassland Plants
Marsh Plants
Herbs and Weeds
CAM Plants
Deciduous Trees
Evergreen Trees and Shrubs
Temperature
Free-Air CO₂ Exchange Studies
Harvest Index
Quality
Yield

Epilogue

References

Index

A Summary appears at the end of each chapter.

"Plenty has been written about concerns over elevated levels of carbon dioxide in the earth¿s atmosphere, but a Kansas State University researcher has found an upside to the higher CO₂ levels. And it¿s been particularly relevant in light of drought that overspread the area in recent months. ¿ The research showed that sorghum and winter wheat used water more efficiently as a result of the increased levels of carbon dioxide in the atmosphere. ¿ Studies done subsequent to the early work confirmed the findings."
¿Mary Lou Peter, K-State Today, March 26, 2013

"This meticulously detailed work describes the literature surrounding plant and soil response to drought and elevated CO^D[2. ¿ Attractive features are the frequent diversions to review the history and fundamental science behind topics under discussion. The volume includes brief biographies of persons of historical importance in the field at the end of each chapter, as well as over 200 high-quality figures. ¿ Summing Up: Recommended."
¿ CHOICE Magazine, May 2012

"This is a book for the specialist/researcher though the explanation of principles, the many examples, and the considerable bibliography also constitute a valuable resource for lecturers. Moreover, the considerable detail on theory and practice is a welcome addition to the global warming literature which is sometimes based more on rhetoric than on tact but at ¿82 it will likely only be a library purchase and then only in a limited number of libraries."
¿ Bulletin of the British Ecological Society, 2011

M.B. Kirkham is a professor in the Department of Agronomy at Kansas State University. Dr. Kirkham is an editorial board member of several journals, including Crop Science and Soil Science. Dr. Kirkham has authored or co-authored over 200 articles in scientific journals and has been a recipient of the Carl Sprengel Agronomic Research Award of the American Society of Agronomy and the Crop Science Research Award of the Crop Science Society of America. Kirkham is a graduate of Wellesley College, Massachusetts, USA.