Environmental factors influencing the structural dynamics of soil microbial communities during assisted phytostabilization of acid-generating mine tailings: A mesocosm experiment

Abstract

Compost-assisted phytostabilization has recently emerged as a robust alternative for reclamation of metalliferous mine tailings. Previous studies suggest that root-associated microbes may be important for facilitating plant establishment on the tailings, yet little is known about the long-term dynamics of microbial communities during reclamation. A mechanistic understanding of microbial community dynamics in tailings ecosystems undergoing remediation is critical because these dynamics profoundly influence both the biogeochemical weathering of tailings and the sustainability of a plant cover. Here we monitor the dynamics of soil microbial communities (i.e. bacteria, fungi, archaea) during a 12-month mesocosm study that included 4 treatments: 2 unplanted controls (unamended and compost-amended tailings) and 2 compost-amended seeded tailings treatments. Bacterial, fungal and archaeal communities responded distinctively to the revegetation process and concurrent changes in environmental conditions and pore water chemistry. Compost addition significantly increased microbial diversity and had an immediate and relatively long-lasting buffering-effect on pH, allowing plants to germinate and thrive during the early stages of the experiment. However, the compost buffering capacity diminished after six months and acidification took over as the major factor affecting plant survival and microbial community structure. Immediate changes in bacterial communities were observed following plant establishment, whereas fungal communities showed a delayed response that apparently correlated with the pH decline. Fluctuations in cobalt pore water concentrations, in particular, had a significant effect on the structure of all three microbial groups, which may be linked to the role of cobalt in metal detoxification pathways. The present study represents, to our knowledge, the first documentation of the dynamics of the three major microbial groups during revegetation of compost-amended, metalliferous mine tailings.

Bacterial Rhizoplane Colonization Patterns of Buchloe dactyloides Growing in Metalliferous Mine Tailings Reflect Plant Status and Biogeochemical Conditions

“…Oxidation of the pyritic tailings in the top 25 cm has produced acidic conditions (pH of 2.3 2.7) [6]. The tailings are characterized by low organic carbon content (0.14 g kg −1 ), hypersalinity (EC 6.5–9.0 ds m −1 ), poor substrate structure [6,7], and the complete absence of vegetation. Both a controlled 1-year greenhouse mesocosm study [7,34] and a 7-year field trial [31] have been conducted to develop phytostabilization strategies for heavy metal containment at this site.…”

“…In addition to being less costly [2,3], phytostabilization is less environmentally destructive because it does not necessitate soil excavation from surrounding lands. However, plant establishment during phytostabilization can be difficult, particularly in weathered pyritic mine tailings under semiarid conditions, due to acidic pH, low organic carbon content, low nutrients, hypersalinity, low moisture, poor substrate structure, and an autotroph-dominated, acid-generating, microbial community [2,4,5,6,7]. Organic amendments are typically required, such as compost, manure, or biosolids, to provide a source of organic carbon and nutrients, pH neutralization, increased water holding capacity, improved aggregate structure, and the addition of a heterotrophic microbial inoculum [2,4,8,9].…”

“…In this study we evaluate rhizoplane and rhizosphere bacterial communities of buffalo plants grown in pyritic tailings from the Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site in Dewey-Humboldt, AZ from previously described mesocosm [7] and field trial [31] experiments. We contend that understanding the factors controlling rhizoplane microbial colonization patterns will provide important insights into the significance of plant-microbe associations to plant survival during phytostabilization of acidic mine tailings.…”

A comparison of technologies for remediation of heavy metal contaminated soils

“…Soil microorganisms are reported to increase root metal contents via increased growth as well as the heavy metal(loid)s immobilization in soil (Rajkumar et al, 2013). Moreover, addition of compost significantly enhances microbial diversity via long-lasting buffering-effect on pH, and consequently allowing plants to germinate and accumulate more heavy metal(loid)s in roots (Valentín-Vargas et al, 2014). Organic and inorganic amendments (natural and synthetic) also facilitate plant-induced immobilization of heavy metal(loid)s in soil (Parra et al, 2016).…”

Plant-Microbe Interactions: A Molecular Approach

“…Many functional traits of the plants act as the modulators of PSF which might adversely affect the plant growth. Soil humidity and partial pressures of entrapped gases also contribute to the selective growth of certain microbes in the ecological sphere (Valentín-Vargas et al 2014 ). Among other environmental factors contributing to the regulation of plant-microbe interaction are agricultural practices, cropping systems, exposure to sunlight, temperature variation, and infestation with herbivorous agents.…”