**Preface to "Genetic Diversity of Soil Bacterial Communities"**

Soil is an important natural resource and has a key role in the biosphere, as most of the carbon and nutrient fluxes occur in the top 10 cm of the soil profile; it is a species-rich habitat that provides support for plant growth and health and consequently affects human activities. Although broadly homogeneous in the landscape, soil is extremely heterogeneous on a microbial scale. In fact, soil supports taxonomic and physiologic microbial diversity, which is regarded as more extensive than that of any other group of organisms and considered vitally important to the maintenance and sustainability of the biosphere.

Soil microbiome has a main role as a driver of the living soil that, in turn, contributes to key life support functions. Anthropogenic activities using soil, such as intensive agriculture, pose a burden on soil functioning. Therefore, it is important to find out good indicators able to detect deleterious changes and thus soil quality.

Looking within the "black box", as soil has been regarded in the last decades, overcoming its inaccessibility, and understanding its microbial composition and functioning, are challenges for scientists. In particular, if it is important to investigate the genetic diversity of microbial populations, it is also fundamental to understand the link between the major functions of microbial biomass and its species composition.

This book investigates the roles that various grass species and their functional forms play in modifying soil bacteriobiome and enzymatic activity, how plant genotypes can influence the bacterial communities related to phosphate mineralization and nitrogen fixation in the rhizosphere, the effects of crops and their cultivation regimes on changes in the soil microbiome and of three different long-term land use intensities on soil biochemical, microbial, and molecular parameters, and reviews how rhizobia, a diverse group of α and β-proteobacteria bacteria, and legume species interact and are responsible for symbiotic biological nitrogen fixation.

> **Carmine Crecchio** *Editor*
