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In tropical forests of southern Ecuador, artisanal gold mining releases heavy metals that become xenobiotic with indefinite circulation and eventual bioaccumulation. Restoration and rehabilitation of degraded mining sites represent a major ecological, technological and economic issue. In this study, we estimate the capacity of two native woody plants to accumulate cadmium (Cd), lead (Pb), zinc (Zn) and mercury (Hg), with the goal of developing effective strategies for phytoremediation of mining sites. Individuals of Erato polymnioides and Miconia sp., as well as their rhizospheric soils, were sampled from a natural zone (NZ) of montane cloud forest, used as a control, and a polluted zone (PZ) subjected to active gold mining. Concentrations of the four heavy metals were analyzed using atomic absorption spectrophotometry. Cd, Zn and Hg concentrations were higher in soils of PZ than NZ. Bioaccumulation (BCF) and translocation factors (TF) showed that Miconia sp. has potential for Cd and Zn phytostabilization, E. polymnioides has potential for Cd and Zn phytoextraction, and both species have potential for Hg phytoextraction. Despite the low productivity of these species, their adaptability to the edaphoclimatic conditions of the region and the possibility of using amendments to increase their biomass could compensate for the effectiveness of these species in reclaiming soils contaminated by mining.

By examining plant responses to heavy metal stress during the early stages of the life cycle, we can predict their tolerance and survival in polluted areas as well as their potential for bioremediation. The objective of our study was to evaluate the effect of exposure to mercury (Hg) on the germination and in vitro development of three plant species: Bidens pilosa, Taraxacum officinale (Asteraceae), and Heliocarpus americanus (Malvaceae). These are wild ecotypes adapted to local edaphoclimatic conditions in southern Ecuador, an area which has been historically affected by artisanal and small-scale gold mining (SSGM). For comparison, we additionally used a known Hg-tolerant plant, Lactuca sativa (Asteraceae). We tested biorelevant concentrations of Hg, equivalent to those occurring in soils affected by SSGM, i.e., up to 4.0 mg/L of Hg. The relative inhibitory effects of the treatments (0.6, 2.0, and 4.0 mg/L of Hg) on the germination percentage were most evident in T. officinale, followed by B. pilosa, while L. sativa and H. americanus were not affected. In terms of the time needed to reach 50% germination (T50), B. pilosa exposed to higher concentrations of Hg showed an increase in T50, while H. americanus showed a significant reduction compared to the control treatment. The reduction in radicle length at 4.0 mg/L Hg compared to the control was more evident in L. sativa (86%) than in B. pilosa (55.3%) and H. americanus (31.5%). We concluded that, in a scenario of Hg contamination in the evaluated concentration range, the grass B. pilosa and the tree H. americanus could have a higher probability of establishment and survival.

Background Artisanal and small-scale gold mining activities are producing contamination with heavy metals and metalloids (HMM) into soils and water worldwide. The HMM are considered as one of the major abiotic stresses due to their long-term persistence in soil. In this context, arbuscular mycorrhizal fungi (AMF) confer resistance to a variety of abiotic plant stressors including HMM. However, little is known regarding the diversity and composition of AMF communities in heavy metal polluted sites in Ecuador. Methods In order to investigate the AMF diversity, root samples and associated soil of six plant species were collected from two sites polluted by heavy metals, located in Zamora-Chinchipe province, Ecuador. The AMF 18S nrDNA genetic region was analyzed and sequenced, and fungal OTUs were defined based on 99% sequence similarity. Results were contrasted with AMF communities from a natural forest and from reforestation sites located in the same province and with available sequences in GenBank. Results The main pollutants in soils were Pb, Zn, Hg, Cd and Cu with concentrations exceeding the soil reference value for agricultural use. Molecular phylogeny and OTU delimitation showed 19 OTUs, the family Glomeraceae was the most OTU-rich followed by Archaeosporaceae, Acaulosporaceae, Ambisporaceae and Paraglomeraceae. Most of the OTUs (11 of 19) have been found at other locations worldwide, 14 OTUs were proven from nearby non-contaminated sites in Zamora-Chinchipe. Conclusion Our study showed that there are no specialized OTUs at the studied HMM polluted sites, but rather generalists adapted to a wide variety of habitats. Their potential role in phytoremediation approaches remains to be investigated.

Las raíces finas, y los hongos micorrícicos arbusculares (HMA) representan estrategias alternativas en la construcción de superficies absorbentes subterráneas, que a su vez constituyen rasgos funcionales clave para los humedales altoandinos. En este trabajo, se comparó la biomasa de raíces finas, el porcentaje, y la anatomía de colonización por HMA en tres humedales (>3000 m.s.n.m.): 1) Jimbura-Amaluza, 2) Tres Lagunas-Yacuambi, y 3) Chinchilla-Saraguro a tres profundidades del suelo (0-10, 10-20 y 20-30 cm). El grado de perturbación geo ecológica relativa es alto en Chinchilla-Saraguro medio en Tres Lagunas-Yacuambi, y bajo en Jimbura-Amaluza. La profundidad tuvo un efecto significativo sobre la biomasa de raíces finas, pero no sobre la colonización micorrícica. La biomasa de raíces finas de 0-10 cm de profundidad en Jimbura-Amaluza fue 57% mayor que en Tres Lagunas-Yacuambi, y 66.7% mayor que en Chinchilla-Saraguro. La colonización micorrícica fue significativamente mayor en los humedales más conservados, que en el humedal menos conservado (Chinchilla-Saraguro). La presencia exclusiva de colonización micorrícica tipo Paris en los tres humedales, coincide con reportes previos en ecosistemas alpinos, y en numerosas plantas con micoheterotrofía parcial (aporte suplementario de carbohidratos provenientes del hongo, en beneficio de la planta). Adicionalmente, en el presente estudio se observaron hongos septados oscuros (HSO) conjuntamente con los HMA, al igual que en otros ecosistemas de gran altitud con condiciones extremas de temperatura, humedad, y radiación. Nuestros resultados mostraron que la biomasa de raíces finas en los primeros centímetros del suelo es altamente susceptible a las perturbaciones, mientras que la colonización micorrícica es menos susceptible. Este estudio contribuye a la comprensión del impacto de las perturbaciones sobre los humedales altoandinos, y proporciona evidencia de la presencia de interacciones bióticas clave para su funcionamiento y sustentabilidad.