Sustainable improvement of soil health utilizing biochar and arbuscular mycorrhizal fungi: A review

Bacterial adaptive strategies to cope with metal toxicity in the contaminated environment - A review.

Production and functionality of exopolysaccharides in bacteria exposed to a toxic metal environment

Since the discovery of mycorrhizas, dogmas have been developed regarding their function, ecology, and distribution. We explore if these dogmas are valid, and if there are research biases toward regions inhabited by most researchers and away from regions inhabited by most plant species. We found, first, that the mycorrhizal status is known in less than 1% of plant species, with few having proven mycorrhizal benefits for growth and development. Second, the mycorrhizal status of a plant species varies within families, even genera. Third, mycorrhizas are important for phosphorus acquisition only within a narrow phosphorus range. Fourth, mycorrhizal plants are not uniform in their response to environment; taxonomy, phylogeny and continental history strongly drive mycorrhizal diversity. For example, the center of diversification of Ericaceae and Orchidaceae is in the neotropics, rather than, as recently claimed, in cold and high-latitude climates. Understanding the importance of mycorrhizas at the family-wide and biome-wide level is therefore conflicted by a research bias toward research-intensive regions outside the phylogenetic hotspots of diversification. The current precepts on mycorrhizas provide important starting points for hypotheses to robustly test when and where mycorrhizas play a role in determining ecological trajectory. The time has come to move forward and revisit past assumptions and update the dogmas, rather than assume functional significance in terms of nutritional benefits from studies on extraneous regions and species. We conclude that non-nutritional benefits deserve far greater attention.

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Revisiting mycorrhizal dogmas: Are mycorrhizas really functioning as they are widely believed to do?

The OCBIL theory comprises a set of hypotheses to comprehend the biota of old, climatically buffered, infertile landscapes (OCBILs). Here, we review evidence from the literature to evaluate the extent to which this theory could apply to the biodiversity hotspot of New Caledonia. We present geological, pedological and climatic evidence suggesting how the island might qualify as an OCBIL. The predictions of OCBIL theory are then reviewed in the context of New Caledonia. There is evidence for a high rate of micro-endemism, accumulation of relict lineages, a high incidence of dioecy, myrmecochory and nutritional specializations in plants. New Caledonian vegetation also exhibits several types of monodominant formations that reveal the importance of disturbances on the island. Fires and tropical storms are likely to be important factors that contribute to the dynamic of New Caledonian ecosystems. Although naturally infertile, there is archaeological evidence that humans developed specific horticultural practices in the ultramafic landscapes of New Caledonia. Further comparisons between New Caledonia and other areas of the world, such as South Africa and Southwest Australia, are desirable, to develop the OCBIL theory into a more robust and generalized, testable framework and to determine the most efficient strategies to preserve their outstanding biodiversity.

Infertile landscapes on an old oceanic island: the biodiversity hotspot of New Caledonia

The ecological restoration of nickel mining-degraded areas in New Caledonia is strongly limited by low availability of soil mineral nutrients, metal toxicity, and slow growth rates of native plant species. In order to improve plant growth for restoration programs, special attention was paid to interactions between plant and soil microorganisms. In this study, we evaluated the influence of inoculation with Curtobacterium citreum BE isolated from a New Caledonian ultramafic soil on arbuscular mycorrhizal symbiosis and growth of Tetraria comosa, an endemic sedge used in restoration programs. A greenhouse experiment on ultramafic substrate was conducted with an inoculum comprising two arbuscular mycorrhizal fungi (AMF) species isolated from New Caledonian ultramafic soils: Rhizophagus neocaledonicus and Claroideoglomus etunicatum. The effects on plant growth of the AMF and C. citreum BE inoculated separately were not significant, but their co-inoculation significantly enhanced the dry weight of T. comosa compared with the non-inoculated control. These differences were positively correlated with mycorrhizal colonization which was improved by C. citreum BE. Compared with the control, co-inoculated plants were characterized by better mineral nutrition, a higher Ca/Mg ratio, and lower metal translocation. However, for Ca/Mg ratio and metal translocation, there were no significant differences between the effects of AMF inoculation and co-inoculation.

Co-inoculation with a bacterium and arbuscular mycorrhizal fungi improves root colonization, plant mineral nutrition, and plant growth of a Cyperaceae plant in an ultramafic soil.

Investigating some mechanisms underlying stress metal adaptations of two Burkholderia sensu lato species isolated from New Caledonian ultramafic soils

The present study focused on the characterization of 10 Curtobacterium citreum strains isolated from the rhizosphere of pioneer plants growing on ultramafic soils from New Caledonia. Taxonomic stat...

Valérie Burtet-Sarramegna

Papers

Co-inoculation with a bacterium and arbuscular mycorrhizal fungi improves root colonization, plant mineral nutrition, and plant growth of a Cyperaceae plant in an ultramafic soil.

Investigating some mechanisms underlying stress metal adaptations of two Burkholderia sensu lato species isolated from New Caledonian ultramafic soils

New Caledonian ultramafic conditions structure the features of Curtobacterium citreum strains that play a role in plant adaptation