Lay summary
Humans are altering the composition of biological communities through a variety of activities that increase rates of species invasions and/or species extinctions, at all scales, from local to global. These changes in components of biodiversity have a strong potential to alter ecosystem properties. In plant communities subordinate species (locally non-dominant species) that collectively compose the main part of the diversity, are generally at greater risk for extinction due their small population sizes. The role of subordinate plant species for the maintenance of ecosystem functions (e.g., production), for the resistance of plant communities against change in resource availability (e.g., drought, fertilization) and for the maintenance of the diversity of belowground organisms (e.g., protists, bacteria, fungi) and their function has recently received increasing attention, but remains poorly known. Understanding the impact of the present loss of biodiversity on ecosystem functions is a key challenge in ecology. If diversity per se can be shown to have a critical role on ecosystem functions, this can be, together with ethical and aesthetic reasons a crucial argument to increase present biodiversity conservation efforts. Moreover, understanding the link between above and belowground diversity is one of the main present challenges in ecology. While this research addresses primarily purely scientific questions, its broader impact on the management of biodiversity and natural plant communities could be significant.Specific aims are:• To assess the role of subordinate plant species on the structure and functioning of the above- and below-ground components of a grassland ecosystem by using a removal experiment.• To assess experimentally the influence of subordinate plant species on the response of above- and belowground components of the ecosystem to resource limitation (drought).• To initiate a long-term experiment in the same site, with possible extension to other ecosystem processes (e.g., nutrient stress release by N or P addition, invasibility) and components (e.g., nematodes, earthworms, flagellates).A field experiment will be carried out on permanent plots in a species-rich grazed meadow of the Swiss Jura Mountains. The effect of subordinate plant species (frequent but never dominant in the plant community) will be assessed through a three-level factor: (1) removal of subordinate plant species; (2) removal of similar biomass of dominant plant species; (3) control without removal. The effect of resource limitation will be assessed through a two-level factor: (1) drought; (2) control. Plant composition, functional traits and biomass will be monitored during the ongoing experiment. Belowground diversity will be identified by monitoring three groups with contrasted functional roles in the soil food web: bacteria, fungi and testate amoebae. Moreover, direct measurements of key soil processes (respiration, decomposition) will be done.