Soil attributes in coal mining areas under recovery with bracatinga (Mimosa scabrella)

Metataxonomy of acid mine drainage microbiomes from the Santa Catarina Carboniferous Basin (Southern Brazil)

Mining activities generate large quantities of wastes that significantly alter the biogeochemistry and ecological structure of entire river basins. Microbial communities that develop in these areas present a variety of survival and adaptation mechanisms. Knowing this diversity at the molecular level is strategic both for understanding adaptive processes and for identifying genomes with potential use in bioremediation and bioprospecting. In this work, prokaryotic and eukaryotic communities were evaluated by meta-taxonomics (16S and 18S amplicons) in sediments and water bodies impacted by acid mine drainage in an important coal mining area in southern Brazil. Five sampling stations were defined on a gradient of impacts (pH 2.7-4.25). Taxon diversity was directly proportional to pH, being greater in sediments than in water. The dominant prokaryotic phyla in the samples were Proteobacteria, Actinobacteria, Acidobacteria, OD1, Nitrospirae, and Euryarchaeota, and among the eukaryotes, algae (Ochrophyta, Chlorophyta, Cryptophyceae), fungi (Basidiomycota, Ascomycota, and Cryptomycota), and protists (Ciliophora, Heterolobosea, Cercozoa). The prokaryotic genera Leptospirillum, Acidithiobacillus, Acidiphilium, Thiomonas, Thermogymnomonas, and Acidobacterium, and the eukaryotic genera Pterocystis and Poteriospumella were associated with more acidic conditions and higher metal concentrations, while the prokaryotic genera Sediminibacterium, Gallionella Geothrix, and Geobacter were more abundant in transitional environments.

Native multispecies and fast-growing forest root biomass increase C and N stocks in a reclaimed bauxite mining area

This study is aimed at evaluating C and N stocks in fractions of soil organic matter (SOM) in an area of bauxite mining under recovery with tree species. We have analyzed the long-term recovery of C and N stocks of organic matter fractions from five types of forest cover (Eucalyptus, Anadenanthera peregrina, mixed plantation of 16 native species, a mined area without vegetation cover as a control site, and a natural forest cover as a reference site). The total organic C (TOC) and N (TN) stocks and also organic matter fractions, particulate organic matter (POM), mineral-associated organic matter (MAOM), microbial biomass (MB), and labile C (LC), were determined, as well as the C/N ratio and the carbon management index (CMI). Although the stocks of TOC and LC, CMI, and MB did not differ between the types of forest cover in the 0-60 cm layer, they were lower than the values in the native forest. Forest cover increases the stocks of TOC, LC, MB, and CMI in the area of bauxite mining compared to the control site. In addition, we found that the TOC C and TN stocks and also SOM fractions (LC, C-MAOM, C-POM, N-MAOM, and N-POM) are positively correlated (r ≥ 0.71 for all cases) with volume of roots larger than 2 mm. Therefore, Eucalyptus, A. peregrina, and a mixed of 16 native trees contribute for restoring stocks of soil C and N following bauxite mining in the Brazilian Atlantic Forest.

In situ restoration of soil ecological function in a coal gangue reclamation area after 10 years of elm/poplar phytoremediation

The soil ecological health risks and toxic effects of coal gangue accumulation were examined after 10 years of elm/poplar phytoremediation. The changes in soil enzyme activities, ionome metabolism, and microbial community structure were analyzed at shallow (5-15 cm), intermediate (25-35 cm), and deep (45-55 cm) soil depths. Soil acid phosphatase activity in the restoration area increased significantly by 4.36-7.18 fold (p < 0.05). Soil concentrations of the metal ions Cu, Pb, Ni, Co, Bi, U, and Th were significantly reduced, as were concentrations of the non-metallic element S. The repair effect was shallow > middle > deep. The soil community structure, determined by 16S diversity results, was changed significantly in the restoration area, and the abundance of microorganisms increased at shallow soil depths. Altererythrobacter and Sphingomonas species were at the center of the microbial weight network in the restoration area. Redundancy analysis (RDA) showed that S and Na are important driving forces for the microbial community distributions at shallow soil depths. The KEGG function prediction indicated enhancement of the microbial function of the middle depth soil layers in the restoration area. Overall, phytoremediation enhanced the biotransformation of soil phosphorus in the coal gangue restoration area, reduced the soil content of several harmful metal elements, significantly changed the structure and function of the microbial community, and improved the overall soil ecological environment.

Does a decrease in microbial biomass alter mycorrhizal attributes and soil quality indicators in coal mining areas under revegetation process?

Losses of microbial diversity in degraded ecosystems still have obscure consequences, especially when considering the interaction between arbuscular mycorrhizal fungi (AMF) and soil bacteria. This study investigates the effect of decreasing microbial biomass on mycorrhizal attributes and soil quality indicators. The dilution-to-extinction approach was applied in microcosms to search for associations among bacterial diversity, mycorrhizal attributes, and soil quality indicators. The experiment was conducted with four soil treatments (undiluted control 10⁰ = D0, 10^-3 = D3, 10^-6 = D6, and 10^-9 = D9) from a short-term (two years = 2Y) and a long-term (15 years = 15Y) coal mine revegetation area. Microcosms were inoculated with 300 spores of Acaulospora colombiana, Gigaspora albida, and Claroideoglomus etunicatum with millet as the host plant. Results included the total number of AMF spores, mycorrhizal colonization, soil aggregation, glomalin, fluorescein diacetate hydrolysis (FDA), basal soil respiration, microbial biomass, and soil bacterial microbiome. Larger differences were observed between areas than between dilution treatments within the sampling area. Attributes that presented differences in the dilutions compared to D0 2Y samples were mycorrhizal colonization (D0 = 85% and D9 = 43.3%), FDA (D0 = 77.2% and D9 = 55.5%), extractable glomalin-related soil protein (D0 = 0.09 and D9 = 0.11) and bacterial diversity (D0 = 7.3 and D6 = 5.3). D0 15Y samples presented differences in microbial biomass nitrogen (D0: 232.0) and bacterial diversity (D0: 7.9, D9: 5.6) compared to the dilutions. Bacterial microbiome present in the D0 samples formed distinct clusters as to other samples and correlated with soil aggregation and basal respiration attributes. Results suggest that AMF inoculation and dilution-to-extinction did not affect soil quality indicators preeminently, but the bacterial community is affected and can influence the process of environmental revegetation. A long-term revegetation period is substantial to improve quality indicators and establish the diversity of microorganisms and consequently revegetation in areas impacted by coal mining.

Short-term effects of land consolidation of dryland-to-paddy conversion on soil CO2 flux

To improve grain production capacity, many areas in the world are shifting from rainfed agriculture to irrigated agriculture. One example of such land consolidation is dryland-to-paddy conversion. The conversion of land use pattern largely affects the stability of farmland soil, especially the soil carbon cycle. However, the mutual feedback mechanisms between carbon flux variation and environmental factors during the farmland consolidation process are still poorly known. Located in the Huang-Huai-Hai Plain China, Xuzhou is a typical area where dryland-to-paddy conversion are most widely distributed. Therefore, in this study, we have carried out dryland-to-paddy conversion by setting up two isolated rectangular fields one group planting corn in dryland (DL) and another group planting in paddy field (PF) in Xuzhou. Here, we determined the effect of dryland-to-paddy consolidation on soil CO₂ flux in two isolated rectangular fields - the dryland (DL) cultivated with corn and the paddy field (PF) cultivated with rice. Our results showed that the soil carbon flux and temperature followed similar unimodal curves with greater soil CO₂ flux of in PF than in DL. Surprisingly, the land conversion significantly reduced soil microbial biomass carbon and easily oxidized organic carbon by 28.55% and 29.09%, respectively. The structural equation modeling results demonstrated that the changes in soil environmental factors, including temperature, and fungal OTU numbers, were the primary drivers for the soil CO₂ flux and soil carbon pool (P < 0.05). Overall, this study improves the understanding of the ecological impact of dryland-to-paddy conversion, providing insights into low-carbon agriculture and climate mitigation.

Molecular Ecological Network Complexity Drives Stand Resilience of Soil Bacteria to Mining Disturbances among Typical Damaged Ecosystems in China

Understanding the interactions of soil microbial species and how they responded to disturbances are essential to ecological restoration and resilience in the semihumid and semiarid damaged mining areas. Information on this, however, remains unobvious and deficiently comprehended. In this study, based on the high throughput sequence and molecular ecology network analysis, we have investigated the bacterial distribution in disturbed mining areas across three provinces in China, and constructed molecular ecological networks to reveal the interactions of soil bacterial communities in diverse locations. Bacterial community diversity and composition were classified measurably between semihumid and semiarid damaged mining sites. Additionally, we distinguished key microbial populations across these mining areas, which belonged to Proteobacteria, Acidobacteria, Actinobacteria, and Chloroflexi. Moreover, the network modules were significantly associated with some environmental factors (e.g., annual average temperature, electrical conductivity value, and available phosphorus value). The study showed that network interactions were completely different across the different mining areas. The keystone species in different mining areas suggested that selected microbial communities, through natural successional processes, were able to resist the corresponding environment. Moreover, the results of trait-based module significances showed that several environmental factors were significantly correlated with some keystone species, such as OTU_8126 (Acidobacteria), OTU_8175 (Burkholderiales), and OTU_129 (Chloroflexi). Our study also implied that the complex network of microbial interaction might drive the stand resilience of soil bacteria in the semihumid and semiarid disturbed mining areas.