ABSTRACT
It is well known that soil organisms, particularly microbiota, play an essential role in the cycling of elements and stabilization of soil structure (1,2). The mineralization of organic matter is carried out by a large community of microorganisms and involves a wide range of metabolic processes. For this reason, it is important to relate ecosystem structure and function to species and functional diversity (3). However, the relationships between genetic diversity and taxonomic diversity are not well understood and even less is known about the manner in which these two properties affect microbial functional diversity (35). Microbial species diversity is related to richness (i.e., the number of different species), evenness (i.e., the relative contribution that individuals of all species make to the total number of organisms present), and composition (i.e., the type and relative contribution of particular species present) (3). According to the well-known and much used BIOLOG approach, microbial functional diversity is related both to the rates of substrate utilization and to the presence or absence of utilization of specific substrates. A decrease in microbial diversity may reduce microbial functionality of soil if “keystone species,” such as nitrifiers and nitrogen-fixing microorganisms, are negatively affected (6). However, this is not generally the rule because rarely are there only a few species that perform a singular function. Several processes, such as organic carbon mineralization, are carried out by a large number of microbial species and a reduction in any group of species has little effect on overall soil processes since other organisms can fulfill these functions (79). This spare capacity or resilience is a feature of most soil ecosystems.
