Microbial community structure and functions during chronosequence-based phytoremediation programme of Lignite tailing soil

The eco-restoration of mine-tailing sites has a profound impact on native microbial communities and soil physicochemical properties. The adaptive response of microbial communities during the initial years of phyto-remediated mine-tailing sites was poorly understood. Therefore, the microbial changes during the early stages of chronosequence-based phytoremediative technology were studied at Lignite mine-tailing soils of Panandhro, Rann (desert) of Kachchh, Gujarat using amplicon and shotgun metagenomic approaches. The mine-tailing regions were segregated into three zones, based on the year of plantation and a fourth zone (i.e. unmined) was in proximity of the mining area. In a successive restoration programme, seedlings of local plant species were randomly dispersed and planted across the study area. The pH was acidic to circumneutral (3.7–6.7) at raw mine-tailing sites, post-revegetation, it retards the soil degradation by stimulating soil pH to 6.5–7.6 with an increase in the period of plantation (i.e. at the fifth year of study). In mine-tailing sites and during the restoration process, the bacterial community was predominantly composed of phyla Firmicutes (32%–72%), Bacteroidetes (1%–10%) and Proteobacteria (1%–24%), with changes in their relative abundances. The annotation of genes and proteins from sequenced metagenomes of different zones revealed the functions related to energy metabolism, cellular processing and signalling, genes for stress response, virulence and defence, various membrane transporters, genetic information processing, organismal systems and metabolism, etc. These results suggested that revegetation in the mine tailings has initiated the primary microbial succession and thus it can be further expanded to the remaining regions of the tailing areas.