How did the ultramafic soils shape the flora of the New Caledonian hotspot?

Abstract

International audienceNew Caledonia is renowned as one of the world's most significant biodiversity hotpots. The nutrient-deficiency and cations imbalances of ultramafic soils, which cover a third of the island, harbor a disproportionally high proportion of the plant diversity and endemism of New Caledonia. This review explores how ultramafic soils have influenced the exceptional endemism and richness of New Caledonia trough the concomitant occurrences of habitat patchiness, climatic instability, environmental gradient, and edaphic heterogeneity of ultramafic soils. We focus on the unique `maquis' vegetation where selective pressures by nutrient deficiency and trace element surplus are at their acme. We aim to synthesize our current understanding of diversification and speciation of lineages that have been phylogenetically studied to date. Fragmentation of the peridotite mantle in isolated massifs, and as such spatial heterogeneity of ultramafic soils types, appear to promote plant endemism and speciation. Repeated independent dispersal events of pre-adapted species and persistence of paleo-endemic lineages have contributed to the phylogenetic diversity and the endemism of the ultramafic flora. Finally, historical climatic instability has caused shifts of rain forest species in refugia thereby favoring the extension of maquis species

Environmental and Geographical Factors Structure Soil Microbial Diversity in New Caledonian Ultramafic Substrates: A Metagenomic Approach

“…Maquis are floristically and physiognomically varied and are often dominated by a single species or few species, in particular by the Myrtaceous plant species that belongs to the genus Tristaniopsis [32]. These plant formations mostly represent secondary vegetation resulting from the degradation of the initial rainforests [33]. The rainforests have been fragmented and currently occupy restricted areas (20% of ultramafic surface).…”

Feral cats threaten the outstanding endemic fauna of the New Caledonia biodiversity hotspot

“…This hotspot (21°30′ S, 165°30′ E) with 270000 inhabitants, located in the southwest Pacific Ocean 1210 km east of Australia, covers 18,576 km 2 and is composed of a main island (16,664 km 2 ) and various satellite islands (Lifou, Maré, Ouvéa, Isles of Pines, Art, Pott, Tiga) (Dubois et al, 1973). The New Caledonia archipelago is, characterized by a large variety of habitats with a mountainous topography and marked climatic and geological contrasts (Isnard et al, 2016). Each habitat harbors very unique species assemblages, and rates of endemism for flora and fauna are especially high because of its geographical isolation and particular ultramafic soils (Grandcolas et al, 2008;Isnard et al, 2016).…”

“…The New Caledonia archipelago is, characterized by a large variety of habitats with a mountainous topography and marked climatic and geological contrasts (Isnard et al, 2016). Each habitat harbors very unique species assemblages, and rates of endemism for flora and fauna are especially high because of its geographical isolation and particular ultramafic soils (Grandcolas et al, 2008;Isnard et al, 2016). The climate is subtropical with average annual temperature varying between 21.9°C and 24.1°C.…”

“…The "Maquis mosaic" is composed of maquis shrubland and rainforest on serpentine soils (A.1). The "Limestone forest" is composed of rainforest on calcareous soils (Isnard et al, 2016).…”

Differential elemental uptake in three pseudo-metallophyte C4 grasses in situ in the eastern USA

“…At high concentrations, as in serpentine soils, trace elements can induce phytotoxicity and reduce plant fitness (Clemens 2001; Lin and Aarts 2012). Many species found in metalliferous sites, called metallophytes, are able to cope with elevated metal concentrations and form unique, endemic plant communities (Baker et al 2010; Faucon et al 2016; Isnard et al 2016). Some plants called pseudo-metallophytes have the ability to grow on both metalliferous and non-metalliferous soils (Pollard et al 2002; Pollard et al 2014).…”