Effects of coal-derived compound fertilizers on soil bacterial community structure in coal mining subsidence areas.

The land damaged by coal mining can be recovered to healthy condition through various reclamation methods. Fertilization is one of the effective methods to improve soil fertility and microbial activity. However, the effects of coal-derived compound fertilizers (SH) on bacterial communities in coal mining subsidence areas still remain unclear. Here, we studied the effects on the nutrient characteristics and bacterial communities in fertilizer-reclaimed soil (CK, without fertilizer; CF, common compound fertilizers; SH, coal-derived compound fertilizers) in coal mining subsidence areas and we applied SH with four different nitrogen application rates (90, 135, 180, and 225 kg/hm2). The results showed that the application of SH significantly increased the contents of available nitrogen (AN), available phosphorus (AP), available potassium (AK), total phosphorus (TP) and soil organic matter (SOM) compared with CK, as well as the bacterial richness (Chao1) and diversity (Shannon) in reclaimed soil that increased first and then decreased with the increase of nitrogen application. Under the same nitrogen application rate (135 kg/hm2), the nutrient content, Chao1 and Shannon of SH2 treatments were higher than those of CF treatment. Meanwhile, SH increased the relative abundance of Proteobacteria, Actinobacteria and Gemmatimonadetes. LEfSe analysis indicated that the taxa of Acidobacteria and Actinobacteria were significantly improved under SH treatments. Canonical correspondence analysis (CCA) and Variance partitioning analysis (VPA) showed that SOM was the most important factor affecting the change of bacterial community structure in reclaimed soil. In conclusion, application of SH can not only increase nutrient content and bacterial diversity of reclaimed soil, but also improve bacterial community structure by increasing bacterial abundance.

Pseudomonas fluorescens with Nitrogen-Fixing Function Facilitates Nitrogen Recovery in Reclaimed Coal Mining Soils.

Coal mining has caused significant soil nitrogen loss in mining areas, limiting reclamation and reuse in agriculture. This article studies the effects of organic fertilizer, inorganic fertilizer, and the combined application of Pseudomonas fluorescens with the ability of nitrogen fixation on soil nitrogen accumulation and composition in the reclamation area of the Tunlan Coal Mine from 2016 to 2022 under the conditions of equal nitrogen application, providing a scientific basis for microbial fertilization and the rapid increase in nitrogen content in the reclaimed soil of mining areas. The results showed that as the reclamation time increased, the nitrogen content and the composition and structure of the soil treated with fertilization rapidly evolved toward normal farmland soil. The soil nitrogen content increased most rapidly in the presence of added P. fluorescens + organic fertilizer (MB). Compared to other treatments (inorganic fertilizer (CF), organic fertilizer (M), and P. fluorescens + inorganic fertilizer (CFB)), MB increased total nitrogen (TN) to normal farmland soil levels 1-3 years earlier. The comprehensive scores of MB and CFB on the two principal components increased by 1.58 and 0.79 compared to those of M and CF treatments, respectively. This indicates that the combination of P. fluorescens and organic fertilizer improves soil nitrogen accumulation more effectively than the combination of P. fluorescens and inorganic fertilizer. In addition, the application of P. fluorescens increases the content of unknown nitrogen (UN) in acid-hydrolysable nitrogen (AHN) and decreases the content of amino acid nitrogen (AAN) and ammonia nitrogen (AN). However, there was no significant effect on the content of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) in soil-mineralized nitrogen (SMN). When combined with inorganic fertilizer, the contribution of SMN to TN increased by 14.78%, while when combined with organic fertilizer, the contribution of AHN to TN increased by 44.77%. In summary, the use of P. fluorescens is beneficial for nitrogen recovery in the reclaimed soil of coal-mining areas. The optimal fertilization method under the experimental conditions is the combination of P. fluorescens and organic fertilizer.

Response of Soil Bacterial Diversity, Predicted Functions and Co-Occurrence Patterns to Nanoceria and Ionic Cerium Exposure.

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.

Transcriptome Profiling Analysis of Phosphate-Solubilizing Mechanism of Pseudomonas Strain W134.

Phosphate-solubilizing bacteria (PSB) can alleviate available phosphorus deficiency without causing environmental pollution, unlike chemical phosphate fertilizers. However, the phosphate solubilization mechanisms of PSB are still unclear. Transcriptome sequencing was used to analyze the expression patterns of differential expressed genes (DEGs) of the phosphate-solubilizing bacterium W134 under the conditions of soluble phosphorus (group A), insoluble phosphorus (group B), and lacking phosphorus (group C). Nine DEGs in three different groups were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Then, high performance liquid chromatography (HPLC) was applied to detect the concentrations and composition of organic acids. Compared with group A, Gene Ontology (GO) annotation showed that the cluster of W134 DEGs in groups B and C were basically the same. Besides, the results of enrichment Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway indicated that genes in the Citrate cycle (TCA cycle) pathway closely related to organic acid production were significantly upregulated. The qRT-PCR results were almost consistent with the expression trends of the transcriptome data. The HPLC results showed that the formic acid, ascorbic acid, acetic acid, citric acid, and succinic acid concentrations were significantly increased in group B and C (p < 0.05), while the contents of lactic acid and malic acid were significantly increased in group B (p < 0.05). The above results provided further validation that the upregulated genes should be related to W134 secretion of organic acids. Our study revealed several potential candidate genes and tried to explain phosphate solubilization mechanisms. This provides a new insight for calcareous reclaimed soil, and it will reduce the need of chemical phosphate fertilizers to promote environmentally friendly agriculture.

Effects of Seven-Year Fertilization Reclamation on Bacterial Community in a Coal Mining Subsidence Area in Shanxi, China.

The restoration of soil fertility and microbial communities is the key to the soil reclamation and ecological reconstruction in coal mine subsidence areas. However, the response of soil bacterial communities to reclamation is still not well understood. Here, we studied the bacterial communities in fertilizer-reclaimed soil (CK, without fertilizer; CF, chemical fertilizer; M, manure) in the Lu'an reclamation mining region and compared them with those in adjacent subsidence soil (SU) and farmland soil (FA). We found that the compositions of dominant phyla in the reclaimed soil differed greatly from those in the subsidence soil and farmland soil (p < 0.05). The related sequences of Acidobacteria, Chloroflexi, and Nitrospirae were mainly from the subsided soil, whereas those of Alphaproteobacteria, Planctomycetes, and Deltaproteobacteria were mainly derived from the farmland soil. Fertilization affected the bacterial community composition in the reclaimed soil, and bacteria richness and diversity increased significantly with the accumulation of soil nutrients after 7 years of reclamation (p < 0.05). Moreover, soil properties, especially SOM and pH, were found to play a key role in the restoration of the bacterial community in the reclaimed soil. The results are helpful to the study of soil fertility improvement and ecological restoration in mining areas.

Effects of fertilization and reclamation time on soil bacterial communities in coal mining subsidence areas.

Land impaired by mining activity can be restored to a productive and healthy state through a variety of reclamation methods. Fertilization is one effective method to improve soil fertility and microbial activity. However, the effects of fertilization and reclamation time on bacterial communities in reclaimed soil remain unclear. Here, we hypothesized that both fertilization and reclamation time could promote restoration of reclaimed soil. To test this, soil properties and bacterial communities in a reclaimed coal mining subsidence area were investigated under different fertilizer regimes and different reclamation times. Compared with no fertilization treatment, fertilization rapidly improved the soil nutrients and bacterial α-diversity, both of which exhibited no significant differences between chemical fertilizer and organic fertilizer. With increasing of reclamation time, the soil nutrient levels (soil organic matter, available nitrogen, available phosphorus, available potassium) and the bacterial diversity increased. Meanwhile, the relative abundances of Proteobacteria, Actinobacteria and Bacteroidetes increased, and the relative abundances of Acidobacteria, Chloroflexi and Nitrospirae decreased. Compared with the 1-year and 3-year reclaimed soils, the soil nutrients and bacterial community structure in the 7-year reclaimed soils were more similar to those in the undisturbed soils. In conclusion, reclamation time is the main driving force for the restoration of soil properties and bacterial communities in mining areas, and fertilization can shorten the recovery time of the reclaimed soil.

Year-round film mulching system with monitored fertilization management improve grain yield and water and nitrogen use efficiencies of winter wheat in the dryland of the Loess Plateau, China.

Year-round film mulching in winter wheat field facilitates rainwater storage in summer fallow period and reduces water evaporation in growing reason, and then increases water use efficiency in the dryland of the Loess Plateau, China. Optimized fertilization further promotes fertilizer utilization efficiencies. In this study, plastic film mulching was extended from plant growth season to summer fallow, and fertilizers were applied by monitoring soil nutrient availability. Field trials were conducted in the dryland of the Loess Plateau over 4 years by using four types of cultivation to investigate the effects of year-round plastic film mulching with monitored fertilization on utilization efficiencies of rainwater and nitrogen (N), and winter wheat yield. The four types of cultivation were farmer practice (FP), ridge-furrow with plastic film mulching system plus conventional fertilization(RPCF), ridge-furrow with plastic film mulching system plus monitored fertilization (RPFM), and flat soil surface with plastic film mulching system plus monitored fertilization (FPFM). Our results indicate that the average yield of winter wheat in RPFM and FPFM treatments was 4491 kg ha-1. Compared with FP treatment, the combined effects of monitored fertilization and film mulching(RPFM and FPFM treatments) could increase grain yield in the range of 24.7 to 42.1%. The film mulching extended to the fallow season increased the water storage in 2 m depth of soil profile, and the amount of soil water storage in the summer fallow period increased by 27 to 30% in FPFM treatment than FP treatment. After 4-year consecutive planting of wheat, the accumulation of nitrate-N in 2 m soil reached 277 kg·ha-1 in the FP treatment, which is 87.7% higher than of the level at the beginning of the experiment. Seventy-five percent of nitrate-N was distributed in the soil layer of 0-120 cm. In addition, the residual nitrate-N showed downward leaching with rainfall during the experiment. The RPFM and FPFM treatments reduced the apparent loss and residual levels of soil N, whereas increased its apparent mineralization compared with FP treatment. The FPFM treatment exhibited a greater utilization of residual nitrate-N from previous years and showed a higher amount of the mineralized N from soil organic matter, therefore leading to a relatively high apparent utilization rate of N (56.7%). Considering both grain yield production and utilization efficiencies of water and N, FPFM with year-round mulching was the most effective cultivation measure for winter wheat in the Loess Plateau.