Changes of nutrients and microbial communities in recovery process of abandoned rare earth tailings

Rare earth elements (REEs) mining has wrought severe ecosystem destruction, particularly in the loss of carbon (C), nitrogen (N), and phosphorus (P). Furthermore, mining effects on nutrient recovery characteristics and associated microbial abundance are still poorly understood. Our aims were to research C, N, and P recovery patterns and microbial communities in abandoned REEs mining tailings with different abandoned durations (AD) of 1.5-year (1.5-Y), 7-year (7-Y), 10-year (10-Y), 14-year (14-Y), and unmined site (CK, the control group) in Jiangxi Province, China. Longitudinal tailings delamination of L1 (0–15 cm) and L2 (15–30 cm) at each site was investigated. During the abandoned duration of rare earth tailings, C and P continued to recover from 1.62 to 8.51 g kg−1 and from 0.71 to 1.94 g kg−1 in the L1 tailing layer. N losses of 0.60 and 0.22 g kg−1 occurred on the 1.5-Y and 10-Y tailings, while N slightly increased in the L1 tailing layer from 10-Y to 14-Y. Mesorhizobium, Methylosinus, Bradyrhizobium, Pseudomonas, and Azospirillum were dominant bacteria in the 14-Y site and in the control. The relative abundances of nitrogen-fixing bacteria Mesorhizobium (32.94%), Sinorhizobium (0.24%), Frankia (0.71%), and Burkholderia (2.38%) in the 14-Y site were 1.33–3.97-times of those in the control (24.19%, 0.18%, 0.32% and 0.60%, respectively), and helpful for tailing N recovery. In the 14-Y site, Tylospora (50.24%), Luellia (11.02%), Tomentella (6.94%), and Chaetomium (4.34%) were the dominant fungi while Tylospora (56.93%), Suillus (11.45%), and Penicillium (6.78%) predominated in the control site. Phosphorus-dissolving fungi (Aspergillus) in the 14-Y site (0.42%) were 4.2-times of those in the control (0.1%), which may have led to the improved P solubility. In the 14-Y site, Woody plants such as Pinus massoniana and native pioneering herbs and ferns such as Dicranopteris dichotoma and Nephrolepis auriculata probably invaded from adjacent areas. We unraveled the natural restoration of plant and microbial communities along with soil nutrient changes on abandoned REEs tailings, thus providing novel insights on ecological recovery and restoration after mining.