Biodiversity and soil health: the role of the soil food web in soil fertility and suppressiveness to soil-borne diseases

The soil food web plays a fundamental role in ensuring key ecosystem processes, maintaining soil fertility and improving soil suppressiveness to soil- borne diseases. The composition and structure of the soil food web reflect the health and condition of soils, and the effects of soil management - including the use of pesticides, fertilizers, tillage, crop rotation and cover crops - on soil functioning and services which can be assessed by the use of soil food web indicators. My presentation focuses on how the assessment of the nature, diversity and the structure of nematode communities allow diagnosing the status of the soil food web and hence soil health. As main components of the soil microfauna involved at different trophic levels and functional guilds, soil nematode communities - including free-living nematodes - provide unique ecological data on soil processes. The high abundance and the large functional and taxonomic diversity of soil nematodes permit the calculation of a number of indicators of soil food web diversity, maturity and condition. The diversity and biomass of nematodes at different trophic levels can be related to different ecosystem services. Nematodes participate in various soil nutrient and energy channels. Bacterial- and fungal-feeding nematodes are used as indicators of the soil food web mineralization service, and indices derived from their abundances and biomass are related to plant productivity and crop yield, while plant-feeding nematodes are used as indicators of below-ground pest pressure. Nematodes from higher functional guilds, i.e., predators and omnivores, act as natural enemies of below-ground pests, and have been found to be excellent indicators of soil suppressiveness to introduced herbivore prey. The joint assessment of such three components of the food web, largely facilitated by recent on-line tools, allows an integral diagnosis of soil health, as well as the on-farm assessment of the effects of crop management on soil functioning. Soil fertility and soil suppressiveness can be promoted by an adequate soil management able to enhance the diversity and the abundance of soil food web organisms.