Understanding and managing soil biodiversity: a major challenge in agroecology

Soils are living environments in which particularly abundant and diverse microbiome and fauna are evolving. The resulting biological functioning has a direct impact not only on soil fertility but also on a series of ecosystems services. Thus, microbial communities are involved in geochemical cycles in which microbial enzymes catalyse the different steps. Modulation of the corresponding activities is essential as these affect plant growth and environmental quality. In general, biodiversity affects both the productivity and stability of agroecosystems. It is therefore of paramount importance to take soil biodiversity and biological functioning into account when designing cropping systems and evaluating their impacts. The progress achieved in soil microbiology in recent years now makes it possible to propose analyses of soil biology, as has been feasible for many years for soil physicochemistry. These analyses obviously require the use of standardized procedures for soil sampling, measuring the abundance and diversity of the microbial communities, as well as the identification of bioindicators. Similarly, referential systems need to be established to interpret these analyses and diagnose the biological status of soils, and, more especially, to determine whether the obtained values are within the range of variations normal for a given soil type and land use. Great progress to standardize such procedures and establish referential systems has been achieved during large-scale research programmes carried out to characterize biodiversity on national and European scales. These diagnostic elements need to be accompanied by recommendations. The aim of ongoing research is thus to propose aids for decision-making, based on the results of biological analyses, so attempts can be made to monitor and manage biodiversity to satisfy soil fertility requirements and ensure the ecosystem services expected of soils.