Microbial Contributions to Biodiversity in Deserts

The number of species living in the soil may well represent the largest reservoir of biodiversity on earth (Giller 1996, Wardle and Giller 1996, Service 1997). Five thousand microbial species have been described and identified (Amann and Kuhl 1998), but the actual number of species may be greater than 1 million (American Society for Microbiology 1994), larger even than the number of insect species (Service 1997). Over the last 10 to 15 years, interest in soil biodiversity has soared, driven by advances in molecular techniques that allow for identification and analysis of soil microbes, many of which are difficult to extract and culture (Kennedy and Gewin 1997). However, the factors that control soil microbial biodiversity and the links between soil biodiversity and ecosystem function are still unclear (Beare et al. 1995, Schimel 1995, Freckman et al. 1997, Brussard et al. 1997, Wall and Moore 1999). Soil may represent an excellent venue for exploring links between biodiversity and ecosystem function. The vast numbers of species in soil and methodological problems have long necessitated a functional approach in soil studies. As a result, soil functions important to organic matter degradation, nutrient cycling, water quality, and air chemistry are well studied (Groffman and Bohlen 1999). As our knowledge of soil biodiversity increases, this information may provide a strong basis for evaluating links between biodiversity and these functions. Evaluating functional diversity of soil communities requires considering how microbes interact with plants and soil fauna to produce patterns of ecosystem processes (Wall and Moore 1999). These interactions vary within and between ecosystems (i.e., across landscapes). Throughout this book, we suggest that the science of biodiversity must consider links to ecosystem processes and interactions with landscape diversity (Shachak et al. this volume). The need for these links is particularly clear when considering soil biodiversity. There have been relatively few studies of microbial processes in desert soils, and very little analysis of desert soil biodiversity (Parker et al. 1984, Schlesinger et al. 1987, Peterjohn 1991, Fließbach et al. 1994, Zaady et al. 1996a,b, Steinberger et al. 1999).