Carbon-fixing microbes can potentially improve soil fertility. However, the potential and function of carbon-fixing microbes remains largely uninvestigated in reclaimed soil of coal-mining subsidence areas. In this study, treatments included UL (uncultivated land), CK (maize cultivation without fertilization), NPK (maize cultivation with chemical fertilizer), M (maize cultivation with manure), MNPK (maize cultivation with manure and chemical fertilizer) after 1-year reclamation in a typical coal mining subsidence area. Quantitative PCR, enzyme-linked immunosorbent assay (ELISA) and high-throughput sequencing were employed to investigate the topsoil carbon-fixing microbial biomass, RubisCO activity and community composition. The results showed that the dominant taxa (i.e., Proteobacteria, Cyanobacteria, Devosia and Marichromatium) were significantly changed after reclamation (P < 0.05). Carbon-fixing microbial community structure in fertilization treatments (NPK, M and MNPK) obviously differed from non-fertilizer treatments (UL and CK). Soil organic carbon and microbial biomass carbon were significantly higher in fertilization treatments than non-fertilizer treatments (P < 0.05). M significantly increased RubisCO activity and cbbL gene abundance (P < 0.05), MNPK significantly increased carbon-fixing microbial richness (P < 0.05). Carbon-fixing microbial community structure was strongly influenced by soil moisture, catalase, total phosphorus and dissolved organic carbon. Some environmental factors indirectly influenced SOC by affecting carbon-fixing microbial biomass, diversity and community structure. Our study implies that even short-term (1-year) reclamation and fertilization could significantly influence carbon-fixing microbial community structure and promote soil carbon accumulation, and the fertilization treatments with manure (M and MNPK) were more conducive, which indicated that carbon-fixing microbes were greatly conducive to improve soil fertility in reclaimed mining areas and achieve carbon neutrality.

Release of nanoceria (nCeO₂) into the environment has caused much concern about its potential toxicity, which still remains poorly understood for soil microorganisms. In this study, nanoceria and cerium (III) nitrate at different doses (10, 100 and 500 mg/kg) were applied to bok choy (Brassica rapa subsp. chinensis), grown in potting soil, to investigate the responses of soil bacterial communities to nanoceria (NC) and ionic cerium (IC) applications. The results showed that bacterial richness was slightly increased in all cerium treatments relative to the negative control without cerium amendment (CK), but a significant increase was only found in IC500. The patterns of bacterial community composition, predicted functions and phenotypes of all NC treatments were significantly differentiated from IC and CK treatments, which was correlated with the contents of cerium, available potassium and phosphorus in soil. The co-occurrence network of bacterial taxa was more complex after exposure to ionic cerium than to nanoceria. The keystone taxa of the two networks were entirely different. Predicted functions analysis found that anaerobic and Gram-negative bacteria were enriched under nanoceria exposure. Our study implies that Proteobacteria and nitrifying bacteria were significantly enriched after exposure to nanoceria and could be potential biomarkers of soil environmental perturbation from nanoceria exposure.

The initial variations in soil bacteria at the very beginning of reclamation still remains unclear. This study investigates the impact on bacterial communities of eight different treatments, including uncultivated land, unfertilized cultivation, chemical fertilizer, chemical fertilizer + bacterial fertilizer, manure, manure + bacterial fertilizer, manure + chemical fertilizer, and manure + chemical fertilizer + bacterial fertilizer, during the short-term reclamation of coal-mining soils. The results showed that total nitrogen, available phosphorus, soil organic carbon, microbial biomass carbon, and alkaline phosphatase activity were significantly increased in all fertilization treatments compared to uncultivated land (p < 0.05). All fertilization treatments other than chemical fertilizer harbored significantly higher activities of urease, catalase, and invertase than unfertilized cultivation (p < 0.05). The bacterial communities structures in manure-amended treatments significantly differed in uncultivated land and unfertilized cultivation and were phylotypically shifted from oligotrophic to Actinobacteria-dominant copiotrophic traits, accompanied with phenotypic succession of the enriching characteristics of Gram-positive, biofilms formation, and stress tolerance. The co-occurrence network in manure-amended treatments harbored a simple co-occurrence network, indicating more productive soils than in no-manure treatments. Manure amendment, total nitrogen, microbial biomass carbon, invertase, catalase, and soil moisture were the key driving factors. Our study underscores the bacterial initialization characteristics promoted by manure at the very beginning of coal-mining reclamation.

Fertilization is an effective measure to rapidly improve soil quality in reclaimed mining areas. However, the combined effects of fertilization regimes and reclamation age on phosphorus (P) fraction transformation and the pqqC-harboring microbial community in reclaimed soils remain unclear. In this study, we investigated the dynamics of inorganic P fractions and the pqqC-harboring bacterial community under different fertilization treatments (no fertilizer: CK; chemical fertilizer: CF; organic manure: M) and reclamation ages (1, 5, and 10 years) in a coal mining reclamation area of Shanxi Province, using long-term field experiments combined with high-throughput sequencing. Results showed that compared with the CF and CK treatments, the M treatment significantly increased soil organic matter (SOM), available P (AP), and total nitrogen (TN) content, and promoted the conversion of moderately labile P (NaOH-Pi) to labile P fractions (H₂O-Pi, NaHCO₃-Pi). Meanwhile, the pqqC gene abundance increased with reclamation age, with the M treatment maintaining the highest levels in all fertilization regimes. Co-occurrence network analysis of core species revealed that the number of connections gradually decreased and the network structure simplified with increasing reclamation age. Correspondingly, the microbial community transitioned from an initial stage characterized by rapid response and intense competition to a stable phase. Specifically, Pseudomonas spp. played a key role in P mobilization. Structural equation modeling (SEM) further demonstrated that reclamation age directly promoted the pqqC gene abundance and AP content, whereas fertilization indirectly influenced P transformation by regulating microbial diversity. Our findings reveal that reclamation age and fertilization synergistically shape the inorganic P profile and the associated bacterial community, providing insights for developing targeted P management strategies in reclaimed lands.