Annals of Botany 91: 939-940, 2003
© 2003 Annals of Botany Company
Van der Heijden, M.G.A. and Sanders, I.R. (eds) Microrhizal ecology
Mycorrhizal ecology
van der Heijden MGA, Sanders IR, eds. 2002.
Berlin: Springer.
Euro 59·95 (softback). 469 pp.
In his foreword to the volume, Philip Grime says: ‘The most significant challenge for ecologists at the present time is to continue to exploit the many current opportunities for penetration into detailed mechanisms but simultaneously to actively promote integration . . . within ecological research. Mycorrhizal ecology is uniquely positioned . . . to provide a lead.’ The volume, edited by van der Heijden and Sanders, thus aims to meet the twin needs of scaling up, from detailed molecular science to the ecosystem, and demonstrating that the plant, as found in nature, is itself a community of organisms that interact with other such communities, and that mycorrhizal fungi are both a common and a longstanding member of that group.
The volume is essentially divided into four major sections. The first section covers the ecophysiology of mycorrhizal plants and the impact of global change on the symbiosis. This section will probably be of most interest to the ecological community. The second section assesses the impact of mycorrhizas on biodiversity and ecosystem functioning, while the third explores the various tropic levels at which mycorrhizal fungi interact with other organisms. The fourth section addresses host specificity, an area where modern molecular techniques are overturning traditional views. The overall aim of the volume is thus to summarize our current understanding of the role of mycorrhizal associations in ecology. The book contains 17 chapters (456 pages excluding the indexes), most written by a team of contributors, and it delivers a substantial treatment which fills an important gap in the current literature.
In an introductory chapter to the volume, David Read (University of Sheffield, UK) reviews the history of mycorrhizal research, putting into context the limits which both reductionist studies and studies carried out in microcosms have made to the understanding of ecology. He concludes that too much current information relates to mycorrhizal functioning under simplified conditions but without clarity on the extent to which functions are expressed in nature. This challenge is however taken up in many of the subsequent chapters.
The first main section begins with a review of the literature on carbon and nutrient fluxes within and between mycorrhizal plants. This goes beyond the transfer of carbon between plants mediated by ecto-mycorrhizal fungi (EMF) and considers a fungal-mediated, via source–sink relationships, and the differences in this role between EMF and arbuscular mycorrhizal (AMF) systems. This theme is extended by a consideration of the influence of the fungal genotype on the amount of P transported to the plant and the amount of C moved across the plant–fungus interface, and by a chapter on the role of foraging strategies of EMF and AMF. This concludes that while the AM growth strategy represents a search for potential new host roots, the EMF strategy reflects optimized nutrient capture when in competition with other mycelia. The ability of mycorrhizal fungi to supply nutrients to the plant must depend on accessing soil nutrients which, in turn, impacts on the cycles of elements, such as N. This is reviewed through a model using information from both stable-isotope and molecular studies, which suggest a major role for mycorrhizal fungi in controlling above-ground ecosystem functioning. The final chapter in this section assesses the likely impact of global change on mycorrhizas, and especially those mediated through plant communities.
The section on biodiversity includes chapters documenting the diversity of EMF and AMF, the links between AMF diversity and ecosystem functioning, AMF as a determinant of plant diversity, and the impact of dynamics within the plant. Together, these chapters document mechanisms by which mycorrhizas can both reduce and increase community diversity. However, the focus of most of the material in these chapters is on carbon and nutrient (N, P) economies. It is disappointing that the role of mycorrhizas, especially AMF, in affecting plant interactions with other fungi is not considered. Although the role of mycorrhizal fungi in influencing plant response to ‘pathogens’ is an agricultural concept, it may have a role in natural ecosystems. The volume contains three chapters detailing the interaction of mycorrhizal fungi with herbivores, soil invertebrates and the interaction of EMF with saprotrophs. As a group, the chapters demonstrate the breadth of impact of AMF at a range of tropic levels. All the chapters consider the evolutionary implications of mycorrhizas.
A key issue in mycorrhizal ecology has been whether most AMF can associate with most plants, and most EMF with a range of tree species, or whether there is a higher level of specificity at the genotype or species level. For EMF and orchidaceous mycorrhizas, a chapter concludes that highly specific interactions occur as a result of mechanisms leading to recognition and rejection meditated by signal molecules and receptor genes. For AMF, Sanders concludes that different fungal taxa have different effects on co-existing plants. He reviews evidence for and against specificity with AMF, but ultimately remains on the fence with the hope that molecular methods may answer the question. Whether these methods will also illuminate the importance of the answer is more uncertain. The volume concludes with a synthesis by its editors of what has gone before. They conclude than an understanding of plant communities is not possible without an understanding of mycorrhizas, and that mycorrhizal fungi have an impact beyond individual plants influencing other organisms and ecosystem functioning.
As might be expected from the Springer Series on Ecological Studies, this volume is well produced, illustrated and has a good index. Inevitably in a multi author volume, an overlap in content occurs between chapters. However, for readers wanting a substantial review of the role of mycorrhizal fungi, AMF and EMF, in ecosystem functioning and soil nutrient cycles, this volume will be a valuable addition to the literature. In his introductory chapter to the volume, David Read laments the lack of mycorrhizal studies involving interactions with saprophytic or pathogen fungi. This identifies a need for a further ecological treatment of mycorrhizas.
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