Resilience of the wheat root-associated microbiome to the disturbance of phenanthrene

Improving soil properties and Sesbania growth through combined organic amendment strategies in a coastal saline-alkali soil

Improving the quality of degraded coastal saline-alkali soil and promoting plant growth are key challenges in the restoration of ecological functions in coastal regions. Organic ameliorants such as effective microbial (EM) agent, biochar, and organic compost have been proposed as sustainable solutions, but limited research has explored the combined effects of these amendments. This study investigates five organic improvement strategies: individual applications of EM, corn straw biochar (CSB), and sewage sludge-reed straw compost (COM), along with combined treatments of CSB + EM and COM + EM, on Sesbania growth in a pot experiment. The results demonstrated that, compared to the separate applications, the combined strategies (CSB + EM and COM + EM) exhibited a greater improvement in Sesbania growth; for instance, the plant dry weight was 4.61-12.1 times that of the control. The improved plant growth was linked to enhanced nutrient uptake and changes in soil properties. The combined strategies, particularly COM + EM, resulted in greater decreases in soil pH (decreased by 2.79%-3.49% compared to the control) and better improvements in soil nutrient content, quantity and quality of dissolved organic matter, microbial community diversity, and the abundance of plant growth-promoting rhizobacteria (PGPR), e.g., Bacillus. Spearman correlation and structural equation modeling confirmed that these soil improvements directly contributed to enhanced plant nutrient uptake. Overall, these findings suggest that combined strategies of COM + EM and CSB + EM, particularly the former, are highly effective for the remediation of coastal saline-alkali soils, offering a promising approach for improving soil fertility and plant productivity in degraded coastal ecosystems.

High phenanthrene degrading efficiency by different microbial compositions construction

Microbial remediation has become the most promising technical means for the remediation of polycyclic aromatic hydrocarbons (PAHs) non-point source contaminated soil due to its low cost of treatment, complete degradation of pollutants, and in-situ remediation. In this study, in order to demonstrate the phenanthrene degrading microbial diversity, phenanthrene was chosen as the representative of PAHs and strains capable of degrading phenanthrene were isolated and screened from the sedimentation sludge and the bottom sludge of oil tank trucks, and high throughput sequencing was used to check the dominant strains with a good degrading effect on phenanthrene. Results showed even more than 50% of phenanthrene was degraded in all samples, the composition of PAH-degrading bacteria was diverse, and different environments constructed different functional microbial groups, which resulted in the microbial adapting to the diversity of the environment. Finally, a series of bacterial species with phenanthrene-degrading functions such as Achromobacter, Pseudomonas, Pseudochelatococcus, Bosea was enriched after nine transferring process. Overall, our study offers value information for the enrichment of functional degrading microbes of phenanthrene or other pollutants that more concern should be paid in not only the degradation rate, but also the diversity variation of microbial community composition.

Co-exposure of microplastics and polychlorinated biphenyls strongly influenced the cycling processes of typical biogenic elements in anoxic soil

The co-exposure of microplastics (MPs) and polychlorinated biphenyls (PCBs) in soil is inevitable, but their combined effect on cycles of typical biogenic elements (e.g. C, N, Fe, S) is still unclear. And the co-exposure of MPs and PCBs caused more severe effects than single exposure to pollution. Therefore, in this study, a 255-day anaerobic incubation experiment was conducted by adding polyethylene microplastics (PE MPs, including 30 ± 10 μm and 500 μm) and PCB138. The presence of PE MPs inhibited the PCB138 degradation. Also, PE MPs addition (1%, w/w) enhanced the methanogenesis, Fe(Ⅲ) reduction, and sulfate reduction while inhibited nitrate reduction and the biodegradation of PCB138. And PCB138 addition (10 mg·kg-1) promoted the methanogenesis and Fe(Ⅲ) reduction, but inhibited sulfate reduction and nitrate reduction. Strikingly, the presence of PE MPs significantly reduced the impact of PCB138 on the soil redox processes. The abundance changes of special microbial communities, including Anaeromyxobate, Geobacter, Bacillus, Desulfitobacterium, Thermodesulfovibrio, Metanobacterium, etc., were consistent with the changes in soil redox processes, revealing that the effect of PE MPs and/or PCB138 on the cycle of typical biogenic elements was mainly achieved by altering the functional microorganisms. This study improves the knowledge of studies on the impact of MPs and combined organic pollutants to soil redox processes, which is greatly important to the stabilization and balance of biogeochemical cycling in ecology.

Combined magnetic biochar and ryegrass enhanced the remediation effect of soils contaminated with multiple heavy metals

Biochar is a very promising material for soil remediation. However, most studies mainly focus on the adsorption ability of biochar on one heavy metal, which is difficult to evaluate the actual remediation effect since soils were contaminated with multiple heavy metals. In order to improve the soil remediation efficiency, we used the joint remediation method of magnetically modified biochar and ryegrass to remediate the soil polluted by compound heavy metals (chromium, nickel, copper, zinc, arsenic and cadmium), and evaluate the effect on the process of organic carbon mineralization in polluted soils. It was found that magnetic biochar and ryegrass together decreased the concentrations of Cr, Ni, Cu, Zn, As, and Cd in soils by 24.12 %, 23.30 %, 22.01 %, 9.98 %, 14.83 %, and 15.08 %, respectively, and reduced the available fractions. Ryegrass roots were the main accumulation part of heavy metals, and the order of enrichment effect was ranked as Zn > As > Cr > Cu > Ni > Cd. In addition, magnetic biochar can maintained the stability of the organic carbon pool, and inhibited the emission of volatile organic compounds from ryegrass. Overall, this study indicates that magnetic biochar spheres combined with ryegrass is an effective method for heavy metals co-contaminated soils, and has the excellent remediation ability for actual co-contaminated soils.

Metabolome regulation and restoration mechanism of different varieties of rice (Oryza sativa L.) after lindane stress

There is a lack of studies on the ability of plants to metabolize chlorinated organic pollutants (COPs) and the dynamic expression changes of metabolic molecules during degradation. In this study, hybrid rice Chunyou 927 (CY) and Zhongzheyou 8 (ZZY), traditional rice subsp. Indica Baohan 1 (BH) and Xiangzaoxian 45 (XZX), and subsp. Japonica Yangjing 687 (YJ) and Longjing 31 (LJ) were stressed by a typical COPs of lindane and then transferred to a lindane-free culture to incubate for 9 days. The cumulative concentrations in the roots of BH, XZX, CY, ZZY, YJ and LJ were 71.46, 65.42, 82.06, 80.11, 47.59 and 56.10 mg·kg-1, respectively. And the degradation ratios on day 9 were 87.89 %, 86.92 %, 94.63 %, 95.49 %, 72.04 % and 82.79 %, respectively. On the 0 day after the release of lindane stress, the accumulated lindane inhibited the normal physiological activities of rice by affecting lipid metabolism in subsp. Indica BH, amino acid metabolism and synthesis and nucleotide metabolism in hybrid CY. Carbohydrate metabolism of subsp. Japonica YJ also was inhibited, but with low accumulation of lindane, YJ regulated amino acid metabolism to resist stress. With the degradation of lindane in rice, the amino acid metabolism of BH and CY, which had high degradation ratios on day 9, was activated to compound biomolecules required for the organism to recover from the damage. Amino acid metabolism and carbohydrate metabolism were disturbed and inhibited mainly in YJ with low degradation ratios. This study provides the difference of the metabolic capacity of the metabolic capacity of different rice varieties to lindane, and changes at the molecular level and metabolic response mechanism of rice during the metabolism of lindane.

Response and adaptation of rhizosphere microbiome to organic pollutants with enriching pollutant-degraders and genes for bioremediation: A critical review

Phytoremediation largely involves microbial degradation of organic pollutants in rhizosphere for removing organic pollutants like polycyclic aromatic hydrocarbons, phthalates and polychlorinated biphenyls. Microbial community in rhizosphere experiences complex processes of response-adaptation-feedback up on exposure to organic pollutants. This review summarizes recent research on the response and adaptation of rhizosphere microbial community to the stress of organic pollutants, and discusses the enrichment of the pollutant-degrading microbial community and genes in the rhizosphere for promoting bioremediation. Soil pollution by organic contaminants often reduces the diversity of rhizosphere microbial community, and changes its functions. Responses vary among rhizosphere microbiomes up on different classes of organic pollutants (including co-contamination with heavy metals), plant species, root-associated niches (e.g., rhizosphere, rhizoplane and endosphere), geographical location and soil properties. Soil pollution can deplete some sensitive microbial taxa and enrich some tolerant microbial taxa in rhizosphere. Furthermore, rhizosphere enriches pollutant-degrading microbial community and functional genes including different gene clusters responsible for biodegradation of organic pollutants and their intermediates, which improve the adaptation of microbiome and enhance the remediation efficiency of the polluted soil. The knowledge gaps and future research challenges are highlighted on rhizosphere microbiome in response-adaptation-feedback processes to organic pollution and rhizoremediation. This review will hopefully update understanding on response-adaptation-feedback processes of rhizosphere microbiomes and rhizoremediation for the soil with organic pollutants.

Combined use of biochar and microbial agent can promote lignocellulose degradation and humic acid formation during sewage sludge-reed straw composting

This study investigated the effects of corn straw biochar (CSB) and effective microorganisms (EM) added individually or combinedly on lignocellulose degradation, compost humification, and microbial communities during sewage sludge-reed straw composting process. All the additive practices were found to significantly elevate the humification degree of compost products. The degradation rates of cellulose, hemicellulose, and lignin in different additive treatments were 20.8-31.2 %, 36.2-44.8 %, and 19.9-25.7 %, respectively, which were greatly higher than those of the control. Compared with the single uses of CSB or EM, the combined use of CSB and EM generated greater promotions in lignin and hemicellulose degradations and increase in humic acid content. By comparing the differences in microbial communities among different treatments, the CSB-EM demonstrated greater increases in activity and diversity of lignocellulose degradation-related microbes, especially for fungus. Lastly, the combined use of CSB and EM was highly recommended as a high-efficient improvement strategy for organic compost production.