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The prevalence of bacterial resistance caused by the application of animal manure has become an important environmental issue. Herein, the vertical migration of antibiotic resistance genes (ARGs) and pathogens in soil and vegetables after the application of different fertilizers was explored. The results showed that the application of composted manure considerably enhanced the abundance of most ARGs and pathogens, especially in surface soil and pakchoi roots. Moreover, the soil ARGs increased partially from log 1.93 to log 4.65 after the application of composted manure, and six pathogens were simultaneously detected. It was observed that the increase in soil depth decreased most ARGs and pathogens by log 1.04-2.24 and 53.98 %~85.54 %, respectively. This indicated that ARGs and pathogens still existed in the deep soil (80-100 cm). Moreover, total organic carbon had a significant influence on the pathogen distribution, whereas bacterial communities primarily drove the vertical migration of ARGs rather than environmental factors. Although most of the ARG-host associations observed in the surface soil were disappeared in deep soil as revealed by network analysis, some co-occurrence pattern still occurred in deep soil, suggesting that some ARGs might be carried to deep soil by their host bacteria. These results were novel in describing the vertical migration of ARGs in the environment after the application of different fertilizers, providing ideas for curbing their migration to crops., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Soil microorganisms promote the recovery of contaminated soil by influencing the cyclic transformation of various substances. In this study, we investigated the impact of mercury pollution on the structure, composition, and main populations of soil microbial communities using a high-throughput sequencing method and observed that mercury pollution significantly influenced the diversity, structure, and distribution pattern of microbial communities. Furthermore, during mercury pollution, the Shannon and Chao indices decreased for the bacterial communities and increased for the fungal communities. Mercury pollution mainly reduced the relative abundances of Proteobacteria (16.2–30.6%), Actinomycetes (24.7–40.8%), and other dominant bacterial phyla. The relative abundance of Ascomycota decreased by 17.4% and 16.7% in alkaline and neutral soils, respectively, whereas the relative abundance of unclassified_k_Fungi increased by 26.1% and 28.6%, respectively. In acidic soil, Ascomycota increased by 106.3% and unclassified_k_Fungi decreased by 71.2%. The results of redundancy and correlation analyses suggested that soil microbial diversity was significantly correlated with soil properties such as pH, cation exchange capacity, soil organic carbon, and total nitrogen (p < 0.05) under different treatments. Our findings highlight the impact of Hg pollution on soil microbial communities, thereby providing a theoretical foundation for the bioremediation of soil Hg pollution. [ABSTRACT FROM AUTHOR]

To probe into the effects of nitrogen (N) fertilizer application strategies on the effects of mercury(Hg)-contaminated soil remediation aiming at clear-cut crop-safe measures, pot experiments were conducted to determine soil properties, microbial communities, and eight experimental treatments were carried out including four kinds of N application strategies respectively in acid and alkaline soils: (1) GK, SK (blank control group); (2) GA, SA (applying readily available N-fertilizer); (3) GS, SS (applying slow-release N-fertilizer); and 4) GB, SB (applying slow-release N-fertilizer plus biochar). The experimental results showed that in contrast with the control group (GK, SK), N fertilization could reduce Hg content in acid soil by 20.47% to 81.60% and 23.38% to 75.74% in alkaline soil; comparing with group GA,SA, GS,SS showed reduction of soil Hg content by 75.96% and 69.86% (in acid soil and alkaline soil), respectively. It was worthwhile to note that the treatment using biochar (GB, SB) had no notable effects on the remediation of Hg contaminated soil, compared with the treatment using slowrelease N fertilizer (GS, SS). In contrast with other treatments, slow-release N fertilizer with biochar considerably impacted the soil microbial community structure, i.e. the microbial abundance of acidic soil increased by 6.23% and the diversity decreased by 11.36%, while these two groups in alkaline soil both showed a downward trend, with a decrease of 17.69% and 16.81% respectively. In regard to the investigation on Hg in leaks, in contrast with the control group, all the N-fertilizer application groups showed that Hg content in leeks edible parts and roots decreased by 20.38% to 66.46% and 20.76% to 35.22% in acid soil, respectively. However, in alkaline soil only slow-release N fertilizer plus biochar group (GB, SB) could remarkably reduced Hg content in edible parts and roots, and compared with group slow-release N fertilizer (GS, SS), declined by 45.05% and 28.15%, respectively. Moreover, according to Spearman correlation analysis, soil pH, organic matter and Hg content were the critical factors affecting the bacterial community. Accordingly, the application of slow-release N-fertilizer was the best choice to diminish soil Hg pollution, and combined applications of slow-release N-fertilizer plus biochar can reduce Hg content in soil and crops; at the same time, significantly boost the microbial abundance specially in acidic soil. In conclusion, the experiments achieved theoretical basis for using different N-fertilizer application strategies to alleviate soil Hg pollution, meantime, probing into the effects of slow-release N-fertilizer plus biochar. [ABSTRACT FROM AUTHOR]