A leguminous species exploiting alpha- and beta-rhizobia for adaptation to ultramafic and volcano-sedimentary soils: an endemic Acacia spirorbis model from New Caledonia

Abstract

Acacia spirorbis subsp. spirorbis Labill. is a widespread tree legume endemic to New Caledonia that grows in ultramafic (UF) and volcano-sedimentary (VS) soils. The aim of this study was to assess the symbiotic promiscuity of A. spirorbis with nodulating and nitrogen-fixing rhizobia in harsh edaphic conditions. Forty bacterial strains were isolated from root nodules and characterized through (i) multilocus sequence analyses, (ii) symbiotic efficiency and (iii) tolerance to metals. Notably, 32.5% of the rhizobia belonged to the Paraburkholderia genus and were only found in UF soils. The remaining 67.5%, isolated from both UF and VS soils, belonged to the Bradyrhizobium genus. Strains of the Paraburkholderia genus showed significantly higher nitrogen-fixing capacities than those of Bradyrhizobium genus. Strains of the two genera isolated from UF soils showed high metal tolerance and the respective genes occurred in 50% of strains. This is the first report of both alpha- and beta-rhizobia strains associated to an Acacia species adapted to UF and VS soils. Our findings suggest that A. spirorbis is an adaptive plant that establishes symbioses with whatever rhizobia is present in the soil, thus enabling the colonization of contrasted ecosystems.

Paraburkholderia atlantica is the main rhizobial symbiont of Mimosa spp. in ultramafic soils in the Brazilian Cerrado biome

“…Contrary to what was expected, none of the isolates were able to grow in culture medium with added Ni, even in the lowest tested concentration. Strains resistant to Ni have already been described in species of the genus Paraburkholderia (Stoppel and Schlegel 1995;Vincent et al 2019). Other examples of bacteria resistant to Ni originating from ultramafic soils are highlighted by Abou-Shanab et al (2006 and Pal et al (2004).…”

“…Alpha and betaproteobacterial symbionts can be associated with leguminous plants in metal-rich soils. Vincent et al (2019) studied the isolates from root nodules of Acacia spirorbis subsp. spirorbis, a mimosoid tree legume endemic to New Caledonia that grows in ultramafic soils, and found bacteria from the genera Paraburkholderia and Bradyrhizobium.…”

Potential of Rhizobia Nodulating Anthyllis vulneraria L. from Ultramafic Soil as Plant Growth Promoting Bacteria Alleviating Nickel Stress in Arabidopsis thaliana L.

“…Consequently, the serpentine syndrome is formed in these soils, which is a specific combination of constraints that exert selective pressure on ultramafic biota [ 1 , 2 ]. Indeed, these soils often support distinctive floras, unique plant communities and soil-born microorganisms that can cope with ultramafic stressful conditions [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. In dry grasslands on ultramafic soils in Poland, representatives of Fabaceae (legumes) are abundant and frequent elements of flora both on natural ultramafic outcrops and ultramafic mine soils [ 11 ].…”