Pontificia Universidad Católica de Chile: Microorganisms that could bring greenness to copper tailings

Every day, the mining industry dumps tons of rock waste materials known as tailings, resulting from the mineral separation process of extractive activity, onto the land. Over time, these sources of pollution – carriers of high concentrations of heavy metals – are abandoned along with the mines that gave rise to them, generating secondary environmental impacts such as the loss of diversity of those beneficial microorganisms for the colonization of plants in degraded soils. .

Faced with the infeasibility of applying conventional remediation technologies in large-scale tailings, a group of researchers from the Center for Applied Ecology and Sustainability, CAPES UC , and the Bioengineering Laboratory of the Adolfo Ibáñe z University , devoted themselves to studying the role they play. the native communities of microorganisms to help the areas covered by abandoned copper tailings to improve the establishment of plants, and thus anticipate the effectiveness in the use of phytoremediation techniques to return the green to these lands.

“Microorganisms play a key role in the establishment of plants, as they degrade organic matter, recycle nutrients and protect plants from stress” – explain the researchers.

To do this, the scientists compared the growth of the native plant of Chile and Argentina known as romerillo (Baccharis linearis ), as well as the composition and dynamics of the microbial community in substrates from two abandoned copper tailings deposits in the Coquimbo region. : Huana and Tambillos, data that were later compared with specimens of B. linearis grown in pots of fresh tailings and surrounding agricultural soil.

The results of the study, published in the journal Scientific Reports , indicated that both the native bacteria of the phyla Actinobacteria, Gammaproteobacteria and Firmicutes, as well as the fungi of the genus Glomus, can favor the acclimatization of this plant in tailings sites, facilitating, over time, changes in vegetation and transformation of mineral substrates in the soil.

“The role of microorganisms in the growth, nutrition and health of plants is increasingly well known,” the researchers explain. “Among other capacities, microorganisms play a key role in the establishment of plants, since they degrade organic matter, recycle nutrients and protect plants from stress.”

However, until now the scope of the microbial community structure, especially at the level of its diversity, in the germination and development of colonizing plants in tailings from large copper mining has not been addressed.

For the CAPES researcher and academic from the Catholic University of Chile, Rosanna Ginocchio , these results contribute to understanding the importance of colonizing these “post-operational” tailings simultaneously, with microorganisms and native plants that spontaneously colonize on these substrates. “Since the tailings are not soils, the baseline of nutrients such as nitrogen and the microorganisms responsible for decomposing the litter that accumulates, is zero. This is how this double colonization will provide the nitrogen from the litter for living plants. The study was key in studying these aspects ”, mentions the co-author of the study.

“These results contribute to understanding the importance of colonizing these“ post-operational ”tailings simultaneously, with microorganisms and native plants that spontaneously colonize on these substrates” – Rosanna Ginocchio, CAPES researcher and UC academic.

Specifically, it was observed that plant growth decreased both in substrates without abundant microbial communities and in fresh tailings that contained different communities. “We discovered that a native microbiota was required to improve the establishment and growth of B. linearis in the tailings, and that the microbial communities were more influenced by the presence of the pioneer plant than by the physicochemical properties of the substrate where it grew”, they comment at work.

“Native (autochthonous) communities are better prepared to interact positively with the plant in this type of substrate than non-native (alien) communities, essentially because they are better adapted,” explains Bernardo González, CAPES researcher and UAI academic , co- study author.

For the biochemist, there are several factors that explain the help that microorganisms provide to plants during their growth and acclimatization: “Most likely, microorganisms help the plant to cope with the toxicity not only of metals, but also of other contaminants present in the soil. Likewise, it is very likely that these native communities help the plant to grow better, regardless of whether the substrate is not the most favorable, ”he concludes.

“It is very likely that these native communities help the plant to grow better, regardless of whether the substrate is not the most conducive” – ​​Bernardo González, CAPES researcher and UAI academic, co-author of the study.

This is the first work to address the diversity analysis of microbial communities in abandoned copper mining tailings. In addition to the results already described, this analysis was also able to shed light on what is driving the diversity of both studied tailings and the microbial communities of B. linearis in the surrounding soils.