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During the last decade, the discipline of soil ecology has experienced an increased relevance. The works of K. Killham (Soil Ecology, 1994, Cambridge University Press) and D. Coleman and D.A. Crossley, Jr. (Fundamentals of Soil Ecology, 1996, Academic Press) are examples of this trend. A new and excellent contribution to the subject is given by Lavelle and Spain in the book Soil Ecology. Their work comprises all the major disciplines that permit the study of soils at an ecological level, with emphasis on the description of functional relationships that occur in the soil system.
The book consists of four main topics organized into four main chapters: The Internal Environment, Microclimate and Resources; Soil Formation; Soil Organisms; and Functioning of the Soil System. The first chapter is an excellent summary of the general properties and attributes of soils. The authors provide insightful information about the major components and environmental conditions of the soil. Solid, liquid, and gaseous phases of the soil system are explained in detail. The mineral solid phase is described in terms of its origin and genesis and its chemical composition, as well as its morphological, physical, and chemical properties. The organic solid phase is briefly discussed as well. Only the essential information about the morphology, functional characterization, and the predominant physical and chemical properties of organic matter are given. Properties and roles of the soil organic fraction are also discussed in the other chapters. The gaseous phase is covered by considering the most important aspects that influence soil biota, such as gas diffusion and anaerobiosis. Carbon dioxide is reviewed in detail, with an explanation of its origin and its chemical and biological significance in the soil environment. The importance of soil structure and microrelief is also addressed. Formation, dynamics, and biological importance of soil aggregates and soil structure are reviewed, with special attention to formation of pores by soil organisms and plants. Soil temperature and soil water are presented as the driving forces of the soil microclimate. Both parameters are described according to their spatial and temporal variations, and their effects in the development of soil organisms and plants. The subsection on hydrological regimes is rather short and would have benefited from greater detail. Inorganic resources are reviewed with a general description of the essential elements. Soil macronutrients, especially C, N, and P, are covered in detail, providing a good understanding of the vast biological processes associated with these elements. Organic resources (i.e., surface litter, soil roots, and soil organic matter) are categorized according to their chemical composition and their spatial and temporal availability for soil organisms.
Soil genesis is described in the second chapter starting with a brief discussion of the master soil horizons at the taxonomic level. Soil forming factors are also explained briefly. Major attention is given to the stages of soil development and major soil-forming processes. The stages are reviewed sequentially, beginning with a complete description of the process of weathering. The second stage corresponds to the formation and accumulation of soil organic matter. It describes the dynamics of accumulation and the factors that regulate the abundance of organic reserves in soils. The third stage is defined as the translocation process. The movement of substances within the soil profile and the corresponding processes that define such movements are adequately covered. The authors pay special attention to the effects of soil fauna (i.e., ants, earthworms, and termites) in the translocation process. Soil erosion is identified as the last stage of soil formation. Geomorphological and accelerated soil erosion are superficially described, and I would have preferred that this topic be discussed in more detail. The major soil-forming processes, or "pedogenetic" processes, are described for tropical, cold, and temperate climates. This description allows a complete understanding of soil-forming processes at a local and regional scale. The examples provided use both the FAO-UNESCO and the U.S. soil taxonomy classification systems, which is particularly beneficial to readers familiar with only one system.
Soil organisms are covered in the third chapter. Microorganisms are described taxonomically as well as in regard to their abundance, biology, and spatial and temporal community structures. There is a clever description of the turnover of microbial biomass, which is called the "sleeping beauty paradox"—the name describes the frequent dormancy of microbial communities and the role of macroorganisms as interruptors of such dormancy. The authors handle soil roots as if they were single organisms. The adoption of such categorization might be controversial, but the biological and ecological importance of roots may allow this point of view. Roots are described morphologically according to the use of soil resources and their spatial distribution. The biology of roots is covered with the study of the processes of uptake of water and nutrients, the resistance of roots to water stress, and the deposition of soluble and insoluble substances (rhizodeposition). Soil invertebrates are reviewed according to their general biology, their ecological categories, density, biomass, and community structure. Emphasis is given to the survival strategies of these organisms given the continuous change of the soil environment. Soil invertebrates are categorized in micro-, meso-, and macrofauna communities. The description of termites and ants is detailed and elaborated, while there is no section dedicated to the influence of vertebrate animals in the soil ecosystem.
Chapter four addresses the soil functional interactions driven by biological agents. The functioning of the soil system is studied at five levels: decomposition of organic substrates, the litter system, rhizosphere, drilosphere, and termitosphere. Decomposition of organic compounds is described as a cascading, hierarchical process where climate is the most important level. This conceptualization allows a complete comprehension of the process of decomposition and the factors that affect it. The litter system is analyzed according to its composition and morphological classification. The discussion is principally focused on the spatial and temporal structures of the litter, the litter-decomposing communities, and the processes and fluxes of organic matter. The next two functional levels are analyzed as microenvironments of intense biological activity. The rhizosphere is described by its spatial extension, biological communities, and the potential processes that occur in it (e.g., nutrient uptake and symbiotic or allelopathic relationships). The analysis of the drilosphere is made through the study of the structure, biology, and distribution of earthworms. This analysis also considers the revision of the physical, biological, and biochemical properties of voids and surrounding space produced by earthworms. The last stage corresponds to the termitosphere or zone of influence of termites. This topic is covered in great detail and constitutes an excellent contribution to the subject. The authors present numerous illustrative figures that help to understand the different topics covered. A few of them need to be improved in the specification of labels and legends.
In summary, the book of Lavelle and Spain is an elaborate study of the properties, factors, and processes that occur in the soil system. Despite the potential complexity of some of the topics, the authors give useful and clear examples that cover a diverse range of soil and climatic conditions. This book will be an important contribution to advanced undergraduate and graduate students, as well as for scientists and researchers working in soil and other environmental sciences.
Department of Crop and Soil Sciences Washington State University Pullman, WA, 99164
jfuentes{at}mail.wsu.edu
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