Book Review: Physiological

The first part of this book is largely an introduction to those aspects of plant physiology that are important for understanding responses to environmental stresses, and covers the subjects growth regulation, plant membranes, phytohormones, carbon balance, and water relations. This part also includes methodological chapters, such as an introduction to plant growth analysis, measurement of plant water relations, and an excellent chapter on the use of stable isotopes in ecophysiological studies of plants. Curiously, no mention is made of methods to measure photosynthesis and respiration. With the exception of the phytohormones chapter, the chapters in this part would make good reading material for introductory courses in physiological plant ecology. The chapter on phytohormones is rather too long and is much less mechanistic in scope than the other chapters in this section. This is clearly partly a reflection of the state of the field, but one wonders whether it was really necessary to illustrate this lack of understanding on 116 pages. Additional methodological chapters are dispersed through the second part of the book, including discussions of techniques to measure irradiance and temperature, as well as a somewhat long treatment of genetic engineering techniques.

The second part of the book covers specific kinds of abiotic stresses, such as drought, flooding, irradiance, and temperature. The excellent treatment of plant water relations is clearly the strong point of this book, reflecting the interest of the first author in this field. These chapters frequently go beyond 'textbook science' to incorporate recent and even controversial topics such as the criticism of the soil-plant-air continuum model of water transport in plants. Many of the examples used are from and systems, such as plants from deserts and Mediterranean climates, and one is occasionally left to wonder how all this may apply to water stress in plants from mesic climates. A similar thought occurred to me when reading the chapter on flooding, which focuses on responses of wetland plants to flooding conditions. How may such responses relate to those exhibited by many non-wetland plants that have to deal with occasional oxygen deficiencies in the soil environment? The chapter on irradiance discusses light levels in the environment and their measurement, responses of photosynthesis and physiological sensors to light, effects of UV radiation, and adaptations to high-fight and low-light conditions and responses to heterogeneous light environments. Photoinhibition is discussed on about three pages, and, again, actual stress responses are only a minor part of this chapter. The chapters on high and low temperatures have a stronger emphasis on stress physiology, but they could serve equally well as general discussions of temperature effects on plant ecophysiology.

The third part of the book contains three chapters on integrative topics. One of these discusses genetic engineering approaches to confer stress tolerance to crop plants. The other two offer a synthesis of stress ecophysiology and discuss multiple stress interactions and generalities, research trends, and future directions. Much of this is written in the style of a discussion chapter in a research paper, in places long-winded and with overuse of phrases such as "this may" and "this suggests", in places gives the impression of hand waving.

So, again, what is this book about? Much of this book deals with plants that are presumably adapted to stressful' conditions, and thus it addresses not only the physiology of plants under stress, but also evolutionary solutions for coping with such conditions. Obviously, because there is no stress-free environment, all plants are to some degree adapted to survive various stresses.

Thus, there is no difference between stress-physiology and physiology, and this is the main message of this book. The authors have chosen to write a textbook about the ecophysiology of plants, in order to help students understand the responses of plants to stress, but somehow they forgot to tell the readers (and perhaps the publisher?) that this is what they were doing. This book is not, as the title would have it, about the physiology of plants under stress, or at least only a small part of it is. Instead, much of the book is devoted to the ecophysiology of plants that grow in environments that would induce stress in plants not adapted to such conditions.

Using a common approach in physiological ecology, the authors "determine appropriate trait combinations that enable plants to cope with a diversity of environmental conditions" (a quote from the introduction), and they do this by inference; for example, the physiological difference between a xerophyte and a mesophyte is interpreted as the adaptive trait syndrome to drought conditions. Lacking other information, this is often a useful approach, but it creates the danger of teleological adaptationist reasoning, and indeed, such reasoning is by no means absent from the book. 'The preface announces that "the significance of evolutionary processes in the development of plant stress responses" is emphasized, but there are no discussions of any kind of evolutionary processes in the book, just frequent references to presumed adaptations. Such loose usage of evolutionary terms occurs throughout; for example, the terms adaptation and acclimation often appear together, giving the impression that these are processes that operate on a similar scale. The difference between phenotypic and genetic change is discussed in the final chapter without a reference to the fact that one takes place within individualals and often within short time periods, while the other, with few exceptions, refers to populations and long periods of time. Few physiological textbooks ever mention evolution outside of the introduction and the authors are to be commended for making the attempt to introduce an evolutionary perspective into the field, but the result in this case does not speak for itself.

A word on design and illustrations: The cover design makes this book blend in with the classic plant physiology textbooks from the 1960s, and the same can be said for the rest of the book design. Figures are mostly adequate to illustrate the concepts discussed in the text, but quite a few are of poor quality, with small symbols that are difficult to distinguish and thin lines and crosshatchings that are virtually invisible (e.g. in figures 5.7 and 6.6).