Nickel (Ni) is a highly demanded metal with multiple uses ranging from the production of metal alloys to electronic components. Currently, low grade ore Ni laterites (i.e. ultramafic derived Ferralsols) currently represent around 50% of mined Ni ores and almost 60% of Ni global resources. Globally, the largest nickel laterite resources are in SE Asia-Australia-Pacific region (from Philippines to New Caledonia). In this region mining has been carried out for more than a century either by public companies or by multinational mining groups (including european companies). Due to its low ore grade, Ni-mining on laterites is highly destructive: strip-mining is developed on wide areas and involves the excavation of the complete soil profile and it generates huge quantities of spoils and tailings.
In addition to its value as sources of metals, Ni laterites are plant biodiversity hotspots that host numerous endemic and threatened species, adapted to the particular conditions of these soils (defficiency in essential plant nutrients, elevated levels of metals…). Thus, restoration of plant communities on Ni-mined ultramafic spoils of this region is especially critical for the maintenance of plant biodiversity. Unfortunately, mining and quarrying activities on ultramafic soils usually exacerbate its harsh conditions for biota, making more difficult the restoration of soil functions and plant communities.
Pioneer species native to ultramafic areas may be a feasible alternative for the restoration of laterite and other ultramafic mine spoils, as they are already adapted to the particular conditions of these soils. Once established, pioneer plants can ameliorate soil conditions as they are able to extract essential nutrients, such as Ca, P, K, from soils, accumulate them in their biomass and then transfer them to the soil in litter organic matter.
Casuarinaceae is a family of pioneer trees and shrubs from the Malesian-Australian-Melanesian region. Two genera of Casuarinaceae (Gymnostoma and Ceuthostoma) are distributed in warm temperate to tropical areas in SE Asia (some Gymnostoma species are also found in New Caledonia), where they act as pioneers on different types of degraded soils, including ultramafic areas. The Casuarinaceae have a very interesting trait for soil restoration: the members of this family form actinorhizal symbioses with Frankia actinobacteria able to fix atmospheric nitrogen, but the bacterial strains in the Casuarinaceae from SE Asia are poorly known.
Some studies have demonstrated that Casuarinaceae trees have improved the chemical fertility of ultramafic soils but produced an important accumulation of recalcitrant litter that limited the colonisation by other species, hampering the restoration efforts.
The project CASUABIOTA was intended to improve our knowledge of soil biota associated to Casuarinaceae from ultramafic areas of SE Asia, with the long-term aim of using these pioneer species on mine restoration. The project had two main
objectives: 1) to advance our knowledge about Casuarinaceae-associated frankiae and its tolerance to nickel, and 2) to obtain insights about the composition of Casuarinaceae litter and the organisms involved in its degradation, with a special interest in earthworms and saprophytic fungi.
