Ecological restoration alters microbial communities in mine tailings profiles

Abstract

Ecological restoration of mine tailings have impact on soil physiochemical properties and microbial communities. The surface soil has been a primary concern in the past decades, however it remains poorly understood about the adaptive response of microbial communities along the profile during ecological restoration of the tailings. In this study, microbial communities along a 60-cm profile were investigated in a mine tailing pond during ecological restoration of the bare waste tailings (BW) with two vegetated soils of Imperata cylindrica (IC) and Chrysopogon zizanioides (CZ) plants. Revegetation of both IC and CZ could retard soil degradation of mine tailing by stimulation of soil pH at 0-30 cm soils and altered the bacterial communities at 0-20 cm depths of the mine tailings. Significant differences existed in the relative abundance of the phyla Alphaproteobacteria, Deltaproteobacteria, Acidobacteria, Firmicutes and Nitrospira. Slight difference of bacterial communities were found at 30-60 cm depths of mine tailings. Abundance and activity analysis of nifH genes also explained the elevated soil nitrogen contents at the surface 0-20 cm of the vegetated soils. These results suggest that microbial succession occurred primarily at surface tailings and vegetation of pioneering plants might have promoted ecological restoration of mine tailings.

Figure 1. Soil chemical and biological properties in the copper mine tailings.

The error bars show the standard error of the three subsamples for each sample of the tailings. TOC, total organic carbon; TN, total nitrogen.

Figure 2. Ordering of the bacterial community composition by non-metric multidimensional scaling (NMDS) using the Bray-Curtis distance index.

The various colors indicate different depths; n = 3. The variance explained by the two first axes is shown in the graph.

Figure 3. Variation partitioning analysis (VPA) was used to determine the effects of soil characteristics, plant species, and depth and interactions between these parameters on the structure of the bacterial community.

Circles without overlap showed the percentage of variation explained by each factor alone. The overlap region of two or three circles displayed the explanation of variation between two or three of these factors.

Figure 4. Relative abundance (percentage) of the main identified bacterial taxonomic groups, i.e., phyla Acidobacteria, Actinobacteria, Bacteroidetes and Firmicutes, classes Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria and Deltaproteobacteria (within the Proteobacteria phylum).

For each tailings sample, the relative abundance of the sequences assigned to a given taxonomic unit was calculated for each of the three subsamples, and the average value was then used to represent the relative abundance of each tailings sample. The error bars show the standard error of relative abundance of the three subsamples for each tailings sample.

Figure 5. Phylogenetic tree of nucleotide nifH sequences in the top 20 cm of tailings.

Additional symbols show the relative frequency (%) of a sequence in the respective clone libraries (○, BW; ◆, IC; ◼, CZ).