The rhizosphere: biochemistry and organic substances at the soil–plant interface. 2nd edn.

Abstract

This book reviews rhizosphere research from approximately the middle of last century to the present. It is a comprehensive coverage of root exudates, specific root–microbial interactions, and nutritional processes in the rhizosphere. The main strength of this second edition is that it is on the topic of the rhizosphere, and despite the many research questions associated with this topic, there are few competing books and it is still an emerging field. Because the field is growing, I suspect it will have a wide readership among root and rhizosphere researchers. Certain chapters to this edition are outstanding, and these include Chapter 1 (Uren) and Chapter 7 (Crowley and Kraemer) because they present critical analyses of rhizosphere processes in field soil. Uren's chapter begins the book with a thorough review of root exudates and their possible functions in soil. It forces the rhizosphere researcher to think about the processes in soil that affect the locations, longevities and activities of exudates, and if they can be expected to function in the field as they do in the laboratory. The phytosiderophore analysis in Chapter 7 is excellent and a good use of a very intensely studied rhizosphere process to illustrate the challenges in identifying such processes that are important in the field. Although not new to this edition, the topics of these chapters are still highly relevant and challenging to the rhizosphere researcher. This second edition includes interesting chapters not present in the first edition. For example, Chapter 14 (Mercier et al.) about gene flow in the rhizosphere is particularly novel and is unique to this book, to my knowledge, and I found it had the most new information. Chapter 5 (Schmidt and Linke) reviews the area of root morphology and architecture, and how they are regulated by nutritional and hormonal signals. In Chapter 6, Varanini and Pinton present an informative coverage of root membrane transporters related to nutrient uptake. This area is expanding rapidly due to gene sequence and protein structure information from model and crop species, and hopefully the third edition will include membrane transporters and receptors related to rhizosphere microbial and root signals. Chapter 11 (Perry et al.) reviews such chemical signals between roots (including allelopathy) and between roots and microorganisms, and this is clearly an exciting area of rhizosphere research. My main criticism about the content of the book, and something the editors may want to think about for a new edition, was that, aside from Chapter 14, the topics of the chapters were essentially ‘traditional’ rhizosphere topics. There are new areas that would each warrant their own chapter, such as biofilms in the rhizosphere, rhizosphere soil structure, water uptake and the spatial and temporal processes that can now be quantified non-invasively with imaging technologies, and the microbial ecology of the rhizosphere determined using DNA-based methods that have dominated soil ecology since the early 1990s. These methods repeatedly suggest a microbial complexity in the rhizosphere that must be addressed by groups working on single organisms in simple, controlled conditions. My more minor criticism is that a couple of the chapters do not present sufficiently challenging and critical views of the topics. The images are in black and white, very poor quality (eg. Fig. 7.4) and are poorly labelled. This is a great shame given, for example, the exciting fluorescent images that are available of root–microbial associations throughout the literature. The publishers should consider a website with colour images to accompany this and future editions if colour printed plates are too expensive. There are typographical errors in the text; these are minor but distracting to the high quality of the content of the book. This book is highly suitable for researchers of roots and rhizospheres, including graduate students. It is a specialized text, and may not initially attract scientists who are not specialized in these areas. However; whole-plant scientists and ecologists interested to see links among rhizosphere processes and plant productivity in managed and natural systems should consider reading this edition. Hopefully this broader, important audience will be more directly reached in the third edition. This review sustains the plant scientist's amazement at all there is yet to discover about the rhizosphere, particularly in real field soils.