Annals of Botany 94/6, © Annals of Botany Company 2004; all rights reserved
Photosynthetic rate and dynamic environment.
Kazutoshi Yabuki, 2004.
Dordrecht/Boston/London: Kluwer Academic Publishers.
50 (hardback). 130 pp.
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The book is a life-history of the author—now Professor Emeritus of Osaka Prefecture University—and his group in science. It is perhaps rare these days that such a personalized text appears as a complete book, not buried within an impersonal volume. Reading it reminded me of papers by Blackman, or Brown and Escombe, written in the late 19th Century, when time and space were freely available to describe the experimental set-up and measurement results in details, and not too many other authors were yet available for citation besides the author's own work. But for this same reason, the book will probably be read with a greater emotional pleasure than alternative, perfect ‘dry science’ texts.
So, what can we learn from the book? ‘Such a breeze, in fact, instills vitality into plants and increases their growth rates’ is written in the Preface, and the rest of the book explains, how this happens.
The short first chapter, ‘A closer look at the wind’, introduces the reader to the concept of the boundary layer: ‘...plant's photosynthetic light response curve is determined by the environmental conditions at the time of measurement, not by the plant's characteristics’ (my italics). The author underestimates the adjustment of the plant characteristics to the environment, focussing on the physical nature of the boundary layer. But such a bias is acceptable. Chapter II is a rather comprehensive treatise of the physics of the leaf boundary layer, describing its methods of visualization, with many pictures of specific cases of different attack angles and wind speeds. Alhough much of this work is similar to heat exchange problems solved in technical science, the link is not emphasized. Most pertinent to plants is the case of a freely vibrating leaf. Alhough lots of complicated specific cases are illustrated, I could not grasp a general message, either in words or in mathematics, which would help me to consider these results in modelling leaf or canopy photosynthesis. Chapter III promises to solve my problem, dealing with ‘Photosynthetic Rate in the Aspects of Leaf Boundary Layer’. Unexpectedly, here the theory is still based on the classical square-root dependence on the ratio of leaf length to the wind speed, while lots of experiments are presented to describe the responses of leaf photosynthesis to wind speed. The author's discomfort is evident when plant characteristics, such as leaf water supply and stomatal resistance, begin to interfere with the well-understood changes of the boundary layer resistance. Noteworthy experiments described are those where leaf photosynthesis clearly depends on the leaf attack angle and, especially, where cucumber plants are artificially vibrated with the aim of increasing their fruit yield. Ingenious experiments, but a more causal analysis is expected. In Chapter IV the subject moves on to ‘Photosynthetic Rate of a Plant Community and Wind Speed’. The reader is introduced to the principles of aerodynamic methods of the measurement of mass transfer between the atmosphere and the plant cover. Historically interesting photographs of pre-computer era equipment and chart recordings are presented with pride. Nevertheless, the result is evident: community photosynthesis depends not only on solar radiation, but strongly on wind speed, even when light is limiting. Perhaps my eyesight was not good enough to distinguish the shapes of the tiny data points, but it seems that in a rice community photosynthesis increased with wind speed in one case (Fig. IV.12), but decreased in the other (Fig. IV.11). The generalization is that the photosynthetic rate of a paddy field and sugarcane field are proportional to the 0·8-power of the wind speed (turbulence), while that in a tropical evergreen forest is proportional to the 0·5-power of the wind speed (laminar flow). The last chapter, ‘Gas Exchange between Pneumatophores and Roots of Mangroves by Photosynthesis of Pneumatophore’ feels like an afterthought, confirming the impression that the book is very much an author's personal report.
This latter aspect alone makes it a wonderful volume. The reader is introduced to a great scientist who has generally been rather in the shade as far as the botanical community is concerned because, although some of his original publications appeared in Agricultural Meteorology, many were in more-or-less local journals. This book is useful reading for everyone who already knows something about photosynthesis, but who wants to know how the movement of the surrounding air influences the gas exchange processes between the air and leaves. I wonder whether this book will encourage the mathematical modelling of plant-community photosynthesis?
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