Physiology is the science of biological processes and functions. Plant physiology had its roots in the early work of Joseph Priestley in 1772 who demonstrated plants give off O2 in the process of photosynthesis but he did not understand that process. Robert Mayer, a German scientist, pointed out in 1845 the significance of C fixation via photosynthesis to the biological world. The world depends on green plants to convert solar energy into organic matter.
Crop physiology, as the basis of understanding crop growth, development, and management, emerged in the 1950s and 1960s replacing the empirical approaches to crop management of previous decades. The CSSA published a landmark volume on crop physiology as a product of an international symposium held at the University of Nebraska in 1969. Knowledge of plant processes and controlling mechanisms increased dramatically during the intervening 24 years since that symposium and it was appropriate to revisit this topic. Hence a symposium was hosted by the University of Florida at Gainesville in 1991. We congratulate the planners and authors from the USA and throughout the world for sharing their authoritative synthesis and views on this intricate topic. The authors have clarified and added detail and insights about crop growth and development, metabolism, and environmental stresses. The advancement of knowledge recorded in this book reflect, in part, the capacity of crop and soil scientists to address expanding concerns of society about the environment and the impact of human activity on our food and fiber production capacity.
This book will enable teachers, researchers, and practitioners to raise new questions, to prepare new knowledge and understanding and to develop' appropriate techniques and solutions to ensure an abundant food and fiber supply while protecting our natural resources. To the organizers, editors, and authors we are indebted and share in their pride of a job well done.
CALVIN D. QUALSET, president
American Society of Agronomy
VERNON B. CARDWELL, president
Crop Science Society of America
LARRY P. WILDING, president
Soil Science Society of America
The international symposium, “Physiology and Determination of Crop Yield,” was held 10–14 June 1991 at the University Centre Hotel, Gainesville, Florida. The Symposium was cosponsored by ASA, CSSA, and SSSA, and was cohosted by the University of Florida/Institute of Food and Agricultural Sciences and the USDA-ARS.
Twenty-five years have passed since the successful 1969 symposium at Lincoln, Nebraska, and resulting book entitled Physiological Aspects of Crop Yield. Scientific knowledge and understanding of physiological and genetic factors influencing crop yield have advanced considerably during that period, aided in part by increased numbers of researchers, new techniques, and new instrumentation. Thus, the goal of the 1991 symposium was to review the scientific advances since 1969, and to integrate the current understanding of physiological processes that influence croP. growth and yield.
At the 1969 symposium, there prevailed a sense of urgency in increasing world food production to feed a rapidly expanding world population as well as an optimism that many future breakthroughs in crop production were possible. The success of the “Green Revolution” dominated the 1969 symposium presentations of genetic and cultural advances to improve production. Between 1969 and the present, the world population has continued to grow and food production has essentially kept pace with population growth, although food distribution remains problematic. While yield potential has continued to rise, optimism is no longer unbounded that it can increase indefinitely. Opinion is mixed on this point: some plant breeders point to the steady rate of genetic gain and propose that this will continue into the future, while others warn that crop yields may be approaching potential limits, limits imposed by light, temperature, water, and season.
Knowledge and understanding of crop growth processes, particularly relative to root, leaf, and seed growth, has increased considerably since 1969. Advances in our insight into metabolic processes have been dramatic, especially for photosynthesis and N2 fixation. The first hints of the C4 photosynthetic pathway were barely comprehended in 1969, but by 1976 whole books were available to explain the new C4 pathway relative to the C3 pathway. Likewise, the O2-fixing behavior of ribulose-1,5 bisphosphate carboxylase-oxygenase was only conclusively resolved by 1971, but has now been thoroughly published in physiology texts. Rather than merely review already well-published photosynthetic pathways, symposium program planners chose to emphasize the regulation and integration of biochemical processes related to photosynthesis, N2 fixation, C metabolism, N metabolism, nutrient uptake, and organ growth.
Environmental stresses, some natural and some man-induced, have become more important limitations to global food production than are inherent physiological limitations. These environmental challenges include: air pollutants, ultraviolet radiation, elevated CO2 concentration, elevated temperature, drought, and low temperature. Crop responses to climate change, air pollution and ultraviolet irradiance were highlighted in this symposium because of their possible impacts on food security and the need to minimize effects of human activities on our environment.
The proposal for the 1991 symposium and book was initiated by T.J. Gerik and K.J. Boote in March 1989 to follow the 1969 symposium and to update the 1969 book with the current state of scientific knowledge. An ad hoc committee of R.M. Shibles (chair), K.J. Boote, J.D. Eastin, R.A. Fischer, T.J. Gerik, D.J. Hume, W.R. Jordan, D.P. Knievel, B. Larkins, R.S. Loomis, B.A. Martin, c.J. Nelson, and L.E. Schrader was appointed to recommend to the CSSA board the possible symposium sites, sponsors, funding sources, and potential topics. The Program Steering Committee [K.J. Boote and T.R. Sinclair (cochairs), S.A. Barber, T.J. Gerik, D.J. Hume, D.P. Knievel, J.M. Norman, and R.M. Shibles] was appointed 13 March 1990 by CSSA President Steve A. Eberhart to plan the program for an international symposium on “Physiology and Determination of Crop Yield.” Local arrangements were handled by T.R. Sinclair, K.J. Boote, and J.M. Bennett.
We express our appreciation to the 210 participants of the symposium, session chairs (D.P. Knievel, D.J. Hume, T.J. Gerik, and R.M. Shibles), speakers, discussants, poster presentors, and those assisting with local arrangements. The symposium and invited speakers were generously supported by ASA, CSSA, SSSA, University of Florida-IF AS (Institute of Food and Agricultural Sciences), USDA-ARS, LI-COR, Inc., Northrup-King Company, Inc., Pioneer Hi-Bred International, Inc., Stoller Chemical Company of Florida, Inc., DeKalb Plant Genetics Foundation, and U.S. Borax Research Corp.
K.J. Boote, coeditor
University of Florida
J .M. Bennett, coeditor
University of Florida
T.R. Sinclair, coeditor
University of Florida
G.M. Paulsen, coeditor
Kansas State University
S. L. Albrecht, Associate Scientist, Department of Agronomy, University of Florida, Gainesville, FL 32611-0840; present position and address is Microbiologist, USDA-ARS, Columbia Plateau Conservation Research Center, Pendleton, OR 97801.
Leon Hartwell Allen, Jr., Soil Scientist, USDA-ARS, and Professor of Agronomy, University of Florida, Gainesville, FL 32611-0846.
Jeffrey S. Amthor, Environmental Scientist, Lawrence Livermore National Laboratory, Livermore, CA 94550.
Roger B. Austin, Institute for Plant Science Research, Cambridge, England; present position is Visiting Scientist at Estacion Experimental de Aula Dei, C.S.I.C., 50080, Zaragoza, Spain
Stanley A. Barber, John B. Peterson Distinguished Professor Emeritus of Agronomy, Purdue University, West Lafayette, IN 47907
J. M. Bennett, Professor, Department of Agronomy, University of Florida, Gainesville, FL 32611-0500.
Dale G. Blevins, Professor of Agronomy, Agronomy Department, University of Missouri, Columbia, MO 65211.
A. J. Bloom, Professor, Department of Vegetable Crops, University of California, Davis, CA 95616.
K. J. Boote, Professor of Agronomy, Agronomy Department, University of Florida, Gainesville, FL 32611.
R. Harold Brown, Professor, Department of Crop and Soil Sciences, University of Georgia, Athens, GA 30602-7272.
Martyn M. Caldwell, Professor of Ecology, Department of Range Science and The Ecology Center, Utah State University, Logan, UT 84322-5230.
Jeremy Colis, Senior Lecturer in Environmental Science, University of Nottingham, England.
Dennis B. Egli, Professor of Agronomy, Department of Agronomy, University of Kentucky, Lexington, KY 40546-0091.
L. T. Evans, CSIRO Division of Plant Industry, Canberra, Australia.
G. D. Farquhar, Professor, Australian National University, Canberra City, Australia.
Stephan D. Flint, Research Associate, Department of Range Science and The Ecology Center, Utah State University, Logan, UT 84322-5230.
Peter J. Gregory, Professor of Soil Science, Department of Soil Science, University of Reading, Whiteknights, P.O. Box 233, Reading, RG6 2DW, England.
Charles L. Guy, Associate Professor, Department of Environmental Horticulture, University of Florida, Gainesville, FL 32611-0512.
J. E. Harper, Supervisory Plant Physiologist, USDA-ARS, Plant Physiology and Genetics Research Unit, University of Illinois, Urbana, IL 61801.
Takeshi Horie, Professor of Crop Science, Laboratory of Crop Science, Faculty of Agriculture, Kyoto University, Kyoto, Japan.
R. J. Jones, Professor/Plant Physiologist, Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108.
David B. Layzell, Professor of Biology, Biology Department, Queen's University, Kingston, Ontario, Canada K7L 3N6.
Paul H. Li, Professor of Horticultural Science and Plant Biological Science, Laboratory of Plant Hardiness, Department of Horticultural Science, University of Minnesota, St. Paul, MN 55108.
Jonathan Lynch, Assistant Professor of Plant Nutrition, Department of Horticulture, Pennsylvania State University, University Park, PA 16852.
Miller B. McDonald, Professor of Agronomy, Department of Agronomy, Ohio State University, Columbus, OH 43210-1086.
Angela H. M. Moloney, Plant Science Department, University of British Columbia, Vancouver, British Columbia, Canada V6T 2B1.
C. Jerry Nelson, Professor of Agronomy, Department of Agronomy, University of Missouri, Columbia, MO.
Henry T. Nguyen, Professor of Plant Genetics, Department of Plant and Soil Science, Texas Tech University, Lubbock, TX 79409.
J. B. Passioura, CSIRO Division of Plant Industry, Canberra, Australia.
Gary M. Paulsen, Professor of Agronomy, Department of Agronomy, Kansas State University, Manhattan, KS 66506.
John W. Radin, National Program Leader for Plant Physiology, USDA-ARS, National Program Staff, Beltsville, MD 20705.
Gina E. Sanders, Lecturer, Department of Life Sciences, Nottingham Trent University, England.
Thomas D. Sharkey, Professor, Department of Botany, University of Wisconsin, Madison, WI 53706.
Robert E. Sharp, Associate Professor of Plant Physiology, Department of Agronomy, University of Missouri, Columbia, MO 65211.
Thomas R. Sinclair, Plant Physiologist, USDA-ARS, and Professor of Agronomy, University of Florida, Gainesville, FL 32611-0840.
Stephen C. Spaeth, Plant Physiologist, Grain Legume Genetics and Physiology Research, USDA-ARS, Pullman, WA 99164-6434.
Judith F. Thomas, Professor of Botany and Director of Phytotron, North Carolina State University, Raleigh, NC 27695-7618.
M. Tollenaar, Associate Professor, Department of Crop Science, University of Guelph, Guelph, Ontario, Canada.
Mike H. Unsworth, Director, Center for Analysis of Environmental Change, Oregon State University, Corvallis, OR 97331-6511.
E. Van Volkenburgh, Associate Professor of Botany, Botany Department, University of Washington, Seattle, WA 98195
Mark E. Westgate, Plant Physiologist, USDA-ARS, MW A, North Central Soil Conservation Research Laboratory, Morris, MN 56267.
E. T. York, Jr., Distinguished Service Professor, University of Florida, Gainesville, FL 32611.