Inderjit, Mallik, A.U. (eds). Chemical ecology of plants: allelopathy in aquatic and terrestrial ecosystems

The study of effects of one plant (including micro‐organisms) on the growth of another plant through the release of low‐molecular compounds (predominantly secondary metabolites) into the environment, defines allelopathy (Rice, 1984). Today, research in allelopathy is conducted by weed scientists, crop scientists, plant ecologists, microbial ecologists, community ecologists, agroecologists and natural products chemists, amongst others, often using an interdisciplinary approach. The number of multi‐author books on the subject has increased in recent years (e.g. Narwal et al., 2000; Kohli et al., 2001; Reigosa and Pedrol, 2002). Despite the numerous studies, doubts that allelopathic interactions occur in situ still exist. Methodological impasses and the complexity of the soil environment are frequently cited as arguments against its occurrence. However, a number of recent ecological case studies provide convincing evidence that keystone species in natural plant communities may actually exert allelopathic effects, through the release of secondary metabolites into the soil, which influence nutrient availability, thus providing new corroborative arguments. In the introductory chapter Mallik and Inderjit present a well‐researched historical survey of allelopathy and introduce the various perspectives and associated problems in the current concept of allelopathy.

Nagle and Wedge review antifungal secondary metabolites from cyanobacteria and algae. Generally, functions of secondary metabolites in algal defence is still a rather unexplored area, although associations of fungi with algae and cyanobacteria in freshwater and marine environments are well documented and some fungi may cause substantial yield losses in sea‐farming cultures of macroalgae. Nagle and Inderjit try to outline possible ecological roles for cyanobacterial secondary metabolites. The production of biotoxins may facilitate maintenance and survival of algal blooms in herbivore‐rich environments, such as coral reefs.

Gallardo‐Williams and Martin focus on phytotoxic compounds from cattail, Typha domingensis. Aromatic and fatty acids may account for growth‐suppressing properties of leachates of the roots and stolons of cattail that become especially dominant in disturbed wetlands. Macías and collaborators review the secondary metabolites that have been isolated from various sunflower species, among them sesquiterpenes, sesquiterpene lactones, diterpenes, triterpenes and flavonoids. Various biological activities are mentioned with a particular focus on in vitro phytotoxicity.

Souto and Pellissier focus on the soil as the environment for allelochemical interactions. They provide arguments for why we have to study soil micro‐organisms in more detail to understand feedback mechanisms that shape plant communities. Kaur, Inderjit and Keating argue that the effect of the substratum should not be neglected in an allelopathy context and illustrate the biotic and abiotic factors that may affect allelochemicals. Nilsen critically evaluates investigations of allelopathy in various habitats, including semiarid chaparral shrubs, subtropical closed canopies as well as temperate and boreal shrubs. To separate allelopathy from competition he suggests imaginative field manipulation experiments. Mallik focuses on the ecosystem level of allelopathy. Studies of conifer regeneration failure in the Northern boreal forest reveal that keystone species of the canopy and soil may act as ecosystem engineers that define habitats by specific allelochemical–nutrient interactions. Jose reviews the controversial viewpoints concerning the activity of juglone, a metabolite of the black walnut tree, one of the classical cases of allelopathy.

Gliessman investigates possible applications of allelopathy in sustainable agriculture. The main goal is not to replace synthetic chemicals by allelochemicals but to view allelopathy as one component in complex interactions in agroecosystems, such as the influence of mixed crop cultures or cover crops on weed control, herbivore resistance, yield improvement and long‐term sustainability. Inderjit and Bhowmik review the potential and limitations of the use of allelochemicals as herbicides. In most of the investigated cases, the majority of which were invasive weeds of fields and pastures, the putative active allelochemicals showed less activity than the crude extract. This and a number of other issues, such as toxicity to non‐target species, limit the application of allelochemicals as herbicides per se. Conversely, cover crops or weed‐suppressing cultivars that release their own allelochemicals may provide a means to combat invasive weeds in crops. Inderjit and Nayyar try to examine the role of abiotic factors that contribute to stress in plants and may thus determine functions of allelochemicals. Koricheva and Shevtsova review the different quantification methods of allelochemicals in plant tissues, and suggest a number of alternative statistical tests to those commonly used.

In the final chapter, Murphy summarizes the current knowledge of allelopathy of pollen. The phenomenon has been found in a number of insect‐ and wind‐pollinated plants including monocotyls and dicotyls. Various classes of secondary metabolites have been isolated from pollen that may exert either stimulatory or inhibitory effects on formation of the pollen tube.

Is this an allelopathy book for biologists? Yes, from my point of view it certainly is. The book is well edited and touches a broad range of topics for all those who want to expand their knowledge regarding interactions between organisms and factors that may contribute to shaping plant communities. I would not, however, consider it a book for students because it demands a certain amount of background knowledge. The choice of topics is well balanced and offers the reader interesting insights into diverse allelopathic phenomena. The sheer diversity of interactions that secondary metabolites are involved in may induce the reader to become more familiar with this plant trait. On the downside, I found that one chapter written by chemists may have the opposite effect because of the too formal presentation of the secondary metabolites and their pharmacological activities. In most of the chapters, a more ample use of illustrations would also add to the information.

In recent years various other books on allelopathy have been published—one that compares with this one is by Reigosa and Pedrol (2002). Both are more aimed at the plant ecologist and ecophysiologist rather than the crop scientist. The price of this book may deter prospective buyers from adding it to their private collection, but this book presents a valuable addition to libraries.

Chemical ecology of plants: allelopathy in aquatic and terrestrial ecosystems.
 Inderjit, Mallik AU (eds). 2002.
 Basel: Birkhäuser Verlag.
 $139, Euro 119·84 (hard cover). 272 pp.