Phytoprotective effect of arbuscular mycorrhizal fungi species against arsenic toxicity in tropical leguminous species.

Arbuscular mycorrhizal fungi (AMF) improve the tolerance of hosting plants to arsenic (As) in contaminated soils. This work assessed the phytoprotective effect of Glomus etunicatum, Acaulospora morrowiae, Gigaspora gigantea, and Acaulospora sp. on four leguminous species (Acacia mangium, Crotalaria juncea, Enterolobium contortisiliquum, and Stizolobium aterrimum) in an As-contaminated soil from a gold mining area. AMF root colonization, biomass production, As and P accumulation, as well as arsenic translocation index (TI) from roots to shoots were measured. The AMF phytoprotective effect was assessed by the P/As ratio and the activity of plant antioxidant enzymes. The AMF colonization ranged from 24 to 28%. In general, all leguminous species had low As TI when inoculated with AMF species. Inoculation of C. juncea with Acaulospora sp. improved significantly As accumulation in roots, and decreased the activity of ascorbate peroxidase (APX) and superoxide dismutase (SOD), highlighting its phytoprotective effect and the potential use of this symbiosis for phytoremediation of As-contaminated soils. However, S. aterrimum has also shown a potential for phytoremediation irrespectively of AMF inoculation. APX was a good indicator of the phytoprotective effect against As contamination in C. juncea and A. mangium. In general P/As ratio in shoots was the best indicator of the phytoprotective effect of all AMF species in all plant species.

Leguminous plants nodulated by selected strains of Cupriavidus necator grow in heavy metal contaminated soils amended with calcium silicate.

Increasing concern regarding mining area environmental contamination with heavy metals has resulted in an emphasis of current research on phytoremediation. The aim of the present study was to assess the efficiency of symbiotic Cupriavidus necator strains on different leguminous plants in soil contaminated with heavy metals following the application of inorganic materials. The application of limestone and calcium silicate induced a significant increase in soil pH, with reductions in zinc and cadmium availability of 99 and 94 %, respectively. In addition, improved nodulation of Mimosa caesalpiniaefolia, Leucaena leucocephala and Mimosa pudica in soil with different levels of contamination was observed. Significant increases in the nitrogen content of the aerial parts of the plant were observed upon nodulation of the root system of Leucaena leucocephala and Mimosa pudica by strain UFLA01-659 (36 and 40 g kg(-1)) and by strain UFLA02-71 in Mimosa caesalpiniaefolia (39 g kg(-1)). The alleviating effect of calcium silicate resulted in higher production of dry matter from the aerial part of the plant, an increase in nodule number and an increase in the nitrogen fixation rate. The results of the present study demonstrate that the combination of rhizobia, leguminous plants and calcium silicate may represent a key factor in the remediation of areas contaminated by heavy metals.