show Abstracthide AbstractNew Caledonia is an archipelago located in the South West Pacific and is recognized has a biodiversity hotspot. One third of this territory is recovered by ultramafic substrates, also called serpentine soils. Ultramafic outcrops harbour diverse vegetation types and remarkable plant diversity. Due to the high concentration of heavy metals in these types of soils, in particular nickel ore, the New Caledonian biodiversity is threatened by the increasing mining activity since more than one century. In this context, the project aim to characterize soil bacterial and fungal diversity in New Caledonian ultramafic substrates, and determine whether floristic composition, edaphic parameters and geographical factors affect this microbial diversity. Such approach will allow us to better understand the ecological functioning of these particular ecosystems and finally will permit to define biological indicators for conservation and ecological restoration purposes.