Format: ORAL

Yohan Pillon1, Juliette Hocedez1, Karine Gotty1, Vanessa Hequet2,3, Sandrine Chay4, Audrey Lopold5, Stphane Dray6

1 Laboratoire des Symbioses Tropicales et Méditerranéennes (LSTM), IRD, INRAE, CIRAD, Institut Agro, Univ. Montpellier, Montpellier, France 2 AMAP, IRD, CIRAD, Herbier de la Nouvelle-Calédonie, Nouméa, New Caledonia 3 AMAP, Univ Montpellier, IRD, CIRAD, CNRS, INRAE, Montpellier, France 4 IPSiM, Univ Montpellier, CNRS, INRAE, Institut Agro, Montpellier, France 5 Institut Agronomique néo-Calédonien (IAC), équipe SolVeg, Nouméa, New Caledonia 6 Université de Lyon, Université Lyon 1, CNRS, VetAgro Sup, Laboratoire de Biométrie et Biologie Evolutive, UMR5558, Villeurbanne, France

High species richness is observed in some shrublands growing on infertile substrates. Mineral nutrients may be the main limiting resources in such ecosystems and underground interactions between plants are probably a key to understand their diversity. Here we tested whether there was a nutritional differentiation between plant species co-occuring in a shrubland in an edaphically extreme environment. We designed a 20 20 m plot in a diverse shrubland (maquis) on ultramafic (infertile) substrate in ew Caledonia. We sampled all 475 plants taller than one meter and we characterised their ionome (22 elements). A total of 37 species were recorded, including a few abundant species and many rare species, representing all major types of mycorrhizal symbioses, nitrogen-fixing plants (actinorhizal but not Fabaceae), cluster rooted and parasitic plants. Both nickel- and manganese-hyperaccumulating species were present in the plot. Using hypervolume approaches, we observed limited overlap in the ionome of the 10 most abundant species. The functionally most distinct species were also the rarest ones in the plot. A diversity of nutritional strategies was represented in the plot, as indicated by the diversity of root symbioses and differences in leaf ionomes. These special nutritional traits associated with adaptation to the infertile substrates meet the expectation of the theory of the Old Climatically Buffered Infertile Landscapes (OCBIL). Our results suggest that partitioning into different biogeochemical niches, including highly specialised ones, could explain the coexistence of a large number of species in this shrubland on infertile substrate.