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Soil acidification poses a significant environmental challenge in China’s southern red soil regions, impacting the abundance of soil microbes and their capacity for carbon fixation. The effect of vegetation types on soil’s biological and abiotic components under acidification, and their regulatory role on the CO2 fixation mechanisms of soil autotrophic microorganisms, is difficult to examine. This gap in understanding constrains the assessment of the carbon fixation potential of red soils. To address this, indoor cultivation coupled with 13C stable isotope labeling was employed to evaluate the disparate abilities of autotrophic microorganisms to assimilate and store CO2 across five vegetation soils from the Qianyanzhou acidic red soil experimental station in China. Findings indicate that carbon fixation rates in these soils spanned from 4.25 to 18.15 mg C kg−1 soil d−1, with paddy field soils demonstrating superior carbon fixation capabilities compared to orchard, coniferous forest, broad-leaved forest, and wasteland soils. The 13C fixation rate in the 0–10 cm soil stratum surpassed that of the 10–30 cm layer across all vegetation types. High-throughput sequencing of 16S rRNA, following cbbL gene purification and amplification, identified Bradyrhizobium, Azospirillum, Burkholderia, Paraburkholderia, and Thermomonospora as the predominant autotrophic carbon-fixing microbial genera in the soil. PERMANOVA analysis attributed 65.72% of the variance in microbial community composition to vegetation type, while soil depth accounted for a mere 8.58%. Network analysis of microbial co-occurrence suggested the soil microbial interactions and network complexity changed with the change of vegetation types. Additionally, multiple linear regression analysis pinpointed the Shannon index and soil organic carbon (SOC) content as primary influencers of carbon fixation rates. Structural equation modeling suggested that iron enrichment and acidification indirectly modulated carbon fixation rates by altering SOC and autotrophic bacterial diversity. This investigation shows the spatial dynamics and mechanisms underpinning microbial carbon fixation across varying vegetation types in southern China’s red soil regions.

To explore the effect of Portulaca oleracea polysaccharides (POP) in regulating intestinal microflora in aged rats in vitro, its intestinal microbial composition was analyzed by 16 S rDNA high-throughput sequencing, and the level of short-chain fatty acids in fermentation broth was determined by LC-MS. POP significantly upregulated the relative abundance of Lactobacillus, Eggerthella, and Paraprevotella and significantly downregulated Escherichia_Shigella, Bacteroides, and Eubacterium nodatum groups. The pH value and ammonia nitrogen level decreased significantly in the POP-treated group, resulting in a more short-chain fatty acid consumption which changed the acid–base environment of the fermentation broth. In conclusion, POP is beneficial to aged rats because it can regulate intestinal flora, promote the growth of probiotics, and inhibit the reproduction of pathogenic bacteria.

Moss-dominated biocrusts are widespread in degraded mining ecosystems and play an important role in soil development and ecosystem primary succession. In this work, the soil microbial community structure under moss-dominated biocrusts in ionic rare earth tailings was investigated to reveal the relationship between different types of moss and taxonomy/function of microbiomes. The results showed that microbial community structure was significantly influenced by four moss species (Claopodium rugulosifolium, Orthotrichum courtoisii, Polytrichum formosum, and Taxiphyllum giraldii). The microbial assembly was more prominent in Claopodium rugulosifolium soil than in the other moss soils, which covers 482 bacterial genera (including 130 specific genera) and 338 fungal genera (including 72 specific genera), and the specific genus is 40% to 1300% higher than that of the other three mosses. Although only 141 and 140 operational taxonomic units (OTUs) rooted in bacterial and fungal clusters, respectively, were shared by all four mosses grown in ionic rare earth tailings, this core microbiome could represent a large fraction (28.2% and 38.7%, respectively) of all sequence reads. The bacterial population and representation are the most abundant, which mainly includes Sphingomonas, Clostridium_sensu_stricto_1, and unclassified filamentous bacteria and chloroplasts, while the fungi population is relatively singular. The results also show that biocrust dominated by moss has a positive effect on soil microbe activity and soil nutrient conditions. Overall, these findings emphasize the importance of developing moss-dominated biocrusts as hotspots of ecosystem functioning and precious microbial genetic resources in degraded rare-earth mining areas and promoting a better understanding of biocrust ecology in humid climates under global change scenarios.

Acidification had a great impact on the aquifer water environment. However, it was not clear how acidification affects aquifer environmental factors and what was the correlation between these environmental factors. So, we studied the effect of simulated acid rain (SAR) on hydrochemical characteristics of red soil aquifer and its correlation analysis. The results showed that SAR caused the pH value of leachate to decline, and the acidification degree of leachate increases significantly with the treatment time. There was a positive correlation between the cumulative release of nitrogen and heavy metals to the environment and the leaching time. Moreover, the leaching of nitrogen and metal ions were affected by filter media, the larger particle size, the higher leaching efficiency. Continuous acidification will affect the transformation of soil nitrogen, activate heavy metals, and increase its harm to soil and groundwater environmental pollution. Further, negative correlations between pH and NH4+-N (r=-0.61; p<0.01), NO2--N (r=-0.80; p<0.01), NO3--N (r=- 0.34; p<0.01), Fe (r=-0.60; p<0.01), Al (r=-0.55; p<0.01), Mn (r=-0.77; p<0.01), Cu (r=-0.42; p<0.01) and Cd (r=-0.65; p<0.01) were found. In addition, the correlation between the leaching rate of three nitrogen and metal ions showed their own characteristics, NH4+-N and NO2--N showed positive correlations with Fe, Al, Mn, Cu and Cd. [ABSTRACT FROM AUTHOR]

A metal-tolerant bacterium strain was isolated from the acidic groundwater of red earth region, located in the Jiangxi province of China. Polyphasic analysis, including a 16S rDNA phylogenetic tree as well as morphological and physicochemical properties, revealed that the isolate was a gram-negative, rod-shaped bacterium, which was recognized as Klebsiella sp. (named H1). Strain H1 had extreme acidity tolerance (pH 2.5) and showed tolerance to heavy metals such as aluminum (Al), iron (Fe) and copper (Cu). It could grow alone in 4 mmol/L Al3+,6 mmol/L Fe3+ and 5 mmol/L Cu2+ at pH 4.0. Strain H1 has the strongest ability to remove aluminum ions (remove Al3+ up to 74.4%), followed by iron ions (remove Fe3+ up to 58.8%), and the relatively weakest ability to remove copper ions (remove Cu2+ up to 48.2%). This is the first discovery that this bacterial species can synergistically resist Al/Fe/Cu toxicity. Although it had a greater impact on ions removal under compound stress, the overall removal effect was better, especially under low concentration treatment. Therefore, Strain H1 can potentially be used as an agent for the bioremediation of metal ions toxicity in acidic soil and groundwater. [ABSTRACT FROM AUTHOR]

A 12-month dynamic analysis concerning the planktonic bacteria and the physicochemical factors of water body in a typical eutrophicated landscape lake was investigated through the use of denatured gradient gel electrophoresis (DGGE). According to the results, the total number of DNA fingerprint bands of the planktonic bacteria were between 18-25 for each month. A seasonal variation was observed as the eutrophication months exhibited a significantly higher proportion in the number of DNA fingerprint bands in comparison to other months. The dominant populations in this landscape water body included Proteobacteria, Actinobacteria, Bacteroides, Planocomycetes, Cyanobacteria, among which Bacteroidetes, Nitrobacteria and Cyanobacteria demonstrated the highest abundance in July and August. When combined with the variation and qualities of water body, it was found that the bacterial diversity was positively correlated with the chemical oxygen demand (COD) and the content of chlorophyll- a, but negatively correlated with dissolved oxygen (DO) and total nitrogen (TN). These findings suggest that there is a close association between microorganism, physicochemical factors of water body and algae. High temperature and high nutrition cause eutrophication of water, improve the diversity of planktonic bacteria, and accelerate the evolution of bacterial population in closed landscape water body. [ABSTRACT FROM AUTHOR]

The pollution of rare earth elements in tailings soil is generally recognized, which is detrimental to the growth of organisms. An yttrium-resistant bacterium, Bl, was isolated from the soil in Longnan rare earth yttrium (Y) mining area, located in the Jiangxi Province of China. Polyphasic analysis, including a 16S rDNA phylogenetic tree as well as morphological and physicochemical properties, revealed that the isolate was a gramnegative, rod-shaped bacterium, which was recognized as Bacillus sp. Bl. Strain Bl is well known for its eosinophilic characteristics, while showing strong tolerance at pH 1.0, with its optimum growth pH value put at 4.0. In general, low concentrations of yttrium stress can promote the growth of the strain Bl. Hence, the growth of the strain Bl was significantly inhibited with an increasing concentration of yttrium stress. In fact, the strain Bl stopped growing when the yttrium concentration increased to l60 mmol/L with the pH of the solution at about 5. Acids can be used to influence the resistance of bacteria to yttrium. The more acidic the medium (low pH), the lower its tolerance to yttrium, with obvious dual stress effect. Research carried out on the tolerance characteristics of strain Bl to rare earth yttrium have also proven that the growth of the bacteria can reduce the yttrium content in solution. Also, that its tolerance to yttrium may have some correlation with the secretion of extracellular polymeric substances (EPS). [ABSTRACT FROM AUTHOR]

The present study reports the impacts of aluminum (Al) on the diversity of archaea in the wild forest soil (FOR, acidic red soil) and long-term cultivated agricultural soil (AGR, near natural red soil). Two types of soil were treated with different Al concentrations (0, 100 or 200 mg Kg-1), respectively for short-term laboratory experiments. Six archaeal 16s rDNA sequence libraries were constructed using the PCR-based RFLP method and the archaeal community characteristics were comparatively analyzed. A total of 58 operational taxonomic units (OTUs) were identified from the six libraries and then sequenced. Blast and phylogenetic analysis revealed that 55.2% of the sequences had the highest similarity with those of the Crenarchaeota and Euryarchaeota phyla, while 44.8% of them were matched to unclassified archaea phylum. Simpson and Shannon indices indicated that Al addition led to the increasing abundance but decreasing evenness of archaea. T-value biplot analysis showed that Al caused the elevation of archaeal abundance in each of soil samples while pH was responsible for the variations of archaeal abundance between two types of soil. Principle component analysis (PCA) suggested that Al was the major factor that affected the diversity of archaea. Redundant analysis (RDA) analysis revealed that the relative abundance of Crenarchaeota was positively correlated with Al, whereas Euryarchaeota was negatively correlated with Al. These results showed that Al improved the diversity of archaea, but was higher in FOR than in AGR, and Crenarchaeota could be more adaptive to the acidic soil and would probably become the dominant phylum if the release of Al3+ continues in the red soil caused by the acid deposition. [ABSTRACT FROM AUTHOR]

Information relating to the effects of Al3+ on soil microbial and enzyme properties is lacking in the studies on acidic red soils. In the present study, under the stress of available Al of Chingkang mountains red soil, such effects were measured by the changes of microbial numbers, enzyme activities (URE and ACP) and microbial biomass carbon (Cmic). The results showed that the microbial numbers, Cmic, ACP and URE activities in the Al-treated samples were significantly lower (p<0.05) than those in control, and clear differences between agricultural soil (AGR soil) and forest soil (FOR soil) were found. The average number of bacteria and fungi was significantly inhibited with an addition of Al3+ higher than 80 mg kg-1 (for bacteria) and 160 mg kg-1 (for fungi), and the decrease in the number of fungus was more prominent in AGR soil than in FOR soil. URE activities decreased significantly only in the early incubation days and were obviously suppressed at the higher level of Al3+ (240 mg kg-1). AGR soil had a lower effect on pH and ACP activities in the case of Al3+ additions than FOR soil. Moreover, a negative correlation was found between monomeric Al concentration and microbial numbers, enzyme activities and soil Cmic. [ABSTRACT FROM AUTHOR]