Community ionomics reveals a diversity of mineral nutrition in a species-rich shrubland on infertile soil

Prepared by Juliette Hocedez, Karine Gotty, Vanessa Hequet, Sandrine Chay, Audrey Léopold, Stéphane Dray & Yohan Pillon

Shrublands are much less studied than tropical rainforests, although they can also support a high level of biodiversity, particularly on soils that are considered barren. This is the case, for example, in New Caledonia, an archipelago in the southwest Pacific, known for its nickel ores. There, metalliferous soils can be covered with rainforests or large areas of a diverse shrubland called “maquis”.

To explain the high diversity of this vegetation we hypothesised that plants differ in the way they exploit the scarce mineral nutrients of the soils. We established a 20 × 20 m plot in a diverse shrubland on an infertile and nickel-rich substrate, where we sampled all plants taller than one metre. Their mineral nutrition was characterised by categorising their root symbioses and measuring their ionome, i.e. all the mineral nutrients and trace elements found in an organism. We measured a total of 22 elements (nitrogen, phosphorus, potassium, nickel, manganese, etc.) in 475 plants.

A total of 37 species were identified in the plot, representing all major forms of mycorrhizal symbioses, as well as nitrogen-fixing plants, cluster-rooted and parasitic plants. Some species showed particularly high leaf concentrations of metals and were qualified as nickel and manganese hyperaccumulators. To understand the ecological niche occupied by the species, we applied a so-called hypervolume approach to our ionomic data to represent their mineral nutrition with a volume of 8 dimensions. We observed that the most abundant species had hypervolumes with limited overlap, suggesting that they use soil nutrients differently. We also observed that the rarest species in the plot had a mineral content that was most different from the others.

The diversity of root symbioses and leaf ionomes observed suggests that many different trophic strategies were present in the plot. Our results suggest that multi-species coexistence in this infertile shrubland may be achieved by species partitioning into different highly specialised biogeochemical niches.

This is a plain language summary of the paper by Juliette Hocedez et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.13301)