Soil as a Support of Biodiversity and Functions

The soil is a major reservoir of biological diversity on our planet. It also shelters numerous biological and ecological processes and therefore contributes to the production of a considerable number of ecosystem services. Among the ecological, social and economic services identified, the role of soil as a reservoir of diversity has now been well established, along with its role in nutrient cycling, supporting primary productivity, pollution removal and storing carbon. Since the development of industrialization, urbanization and agriculture, soils have been subjected to numerous variations in environmental conditions, which have resulted in modifications of the diversity of the indigenous microbial communities. As a consequence, the functional significance of these modifications of biodiversity, in terms of the capacity of ecosystems to maintain the functions and services on which humanity depends, is now of pivotal importance. The concerns emanating from the scientific community have been reiterated in the Millennium Ecosystem Assessment (MEA, 2005) published by the policy makers. This strategic document underlines the need to consider biodiversity as an essential component of ecosystems, not only because of its involvement in providing services essential to the well-being of human societies but also because of its intrinsic value in terms of a natural patrimony that needs to be preserved. This objective cannot be raised without the improvement of our ability to predict the effects of environmental changes on soil biodiversity, ecosystem functioning and the associated services; this requires a better quantification of soil biodiversity at different temporal and spatial scales, and its translation into biological functioning. Major advances in molecular biology since the mid-1990s have allowed the development of techniques to investigate and resolve the diversity of soil microbial communities (Maron et al., 2007). This chapter describes present and ongoing conceptual and methodological strategies employed to assess and understand better the distribution and evolution of soil microbial diversity at different spatial and temporal scales. It also presents actual knowledge about the link between soil microbial diversity and soil processes, with emphasis on C and N cycling, which are determinant for many of the ecosystem services.