Since about the age of ten, I have been fascinated by plants and their use for decoration as flowers, and for food. Much of my pocket money as a child came from the sale of plants and flowers and I quickly learned the practical benefits to be gained from controlling soil fertility in the garden and from good quality potting media in the glasshouse. It was this interest in plants, together with the misery of the famine in India during my teenage years, which led me to study soil science at the University of Reading, although my interest in plants was temporarily put on hold as much of my degree was essentially chemistry. For my PhD at Nottingham University, I was able to choose a topic that interested me, and after a false start on the kinetics of phosphate adsorption by soil minerals, I came across two papers in the library, one by Glyn Bowen and Albert Rovira, and the other by Howard Taylor and Betty Klepper, which enthused me with the possibility of combining my interests in plants and soils by studying roots and their interactions with soil. I quickly found that roots in soil were difficult to study, not least because they cannot be seen, but the satisfaction of patient discovery was considerable. The early encouragement in this endeavour by my supervisors David Crawford and Mike McGowan was essential, as was that of those who eventually became co-workers and colleagues, John Monteith, Paul Biscoe and Nick Gallagher.

Much of my professional career has been spent at the University of Reading where I was allowed the freedom by Alan Wild to continue and build my studies on root:soil interactions. Projects in the UK and overseas followed, and with a succession of PhD students and postdoctoral research workers I have been able to work on a wide range of crops and practical problems, all with a basis in the growth and activity of root systems. When I started my work, the emphasis was on how various soil properties affect the plant and its ability to take up water and nutrients, but recently the emphasis has changed, as it has come to be appreciated that plant roots also change the properties of soils and are not merely passive respondents.

The idea for this book first came in a conversation with my friend Rod Summerfield but for various reasons, including a career change in Australia, it is only now that I have had the determination to bring the project to a conclusion. In fact, I think it is a better book as a result because I believe that the recent development of techniques and the improved understanding of root:soil interactions make this a particularly exciting time to try and write such a book. I have tried to draw together information from diverse elements of the plant and soil literatures to illustrate how roots interact with soil, both to modify it and to obtain from it the resources required for the whole plant to grow. My emphasis has been on whole plants and root systems, although I have drawn on the growing body of literature at plant molecular and cellular levels as appropriate

A particular difficulty in the writing has been that roots of relatively few plant species have been studied and of these most are cereal crops such as maize and wheat. This means that the desire to generalize findings as one might in an introductory undergraduate textbook has had to be tempered with an appreciation of the paucity of information. I hope that I have been able to convey useful principles while at the same time indicating that plant species other than those studied might respond differently. A second area of caution is that many studies in the plant literature have been conducted on young, seedling roots in solutions or in non-soil media. Extrapolation of such findings to older plants, with roots of different anatomy, with fungal and bacterial associations, and with gradients of solutes and gases resulting from past activity, must be undertaken cautiously. Finally, there has been until recently a tendency to regard all roots on a plant as anatomically similar and functionally equivalent; this notion is beginning to be challenged as results indicating particular arrangements of cell types and functional specialisms appear. Measurements are few at present, but we may yet find that roots within a root system make particular contributions to the activities of the whole.

So, this is a personal view of the subject aimed at those who already have a background knowledge of soils and plants. Besides those I have already mentioned, I should like to thank Christopher Mott, Bernard Tinker, Dennis Greenland, Peter Cooper, Lester Simmonds, Ann Hamblin, Neil Turner and Derek Read for sustaining my enthusiasm in root studies at various points in my career, and to thank Michelle Watt, Glyn Bengough, Margaret McCully, John Passioura, Rana Munns, Sarah Ellis, Steve Refshauge, Mark Peoples, Ulrike Mathesius, Sally Smith, Ken Killham, Philippe Hinsinger, Richard Richards, Greg Rebetzke, Tim George, Manny Delhaize, Wolfgang Spielmeyer and John Kirkegaard for reading and suggesting improvements to various parts of the manuscript. I am very grateful to the University of Reading for giving me study leave to undertake this project, and to the Leverhulme Trust for a Study Abroad Fellowship that enabled me to spend a very productive period in Canberra, Australia. As ever, CSIRO Division of Plant Industry, Australia provided a challenging academic environment in which to work (my thanks to the Chiefs Jim Peacock and Jeremy Burdon) and I am indebted to Carol Murray and her staff, especially Michelle Hearn, at the Black Mountain Library for helping me locate reference materials. Finally, my thanks to my personal assistant, Tricia Allen, the staff of the ITS unit at the University of Reading and Ian Pitkethly at SCRI for help with the figures, and to Nigel Balmforth and the staff at Blackwell Publishing for seeing the manuscript through to publication.

Peter J. Gregory

Plant Roots: Growth, Activity and Interaction with Soils

Peter J. Gregory Copyright © 2006 Peter Gregory

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