Conversion of swine manure into biochar for soil amendment: Efficacy and underlying mechanism of dissipating antibiotic resistance genes.

Livestock manure amendment, a common fertilization method for agricultural practice, can exacerbate antibiotic resistance gene (ARG) pollution, thus threatening food safety and human health. On the other hand, manure can also be produced as biochar to improve soil quality, which may reduce ARGs inside manure. However, it is unclear how and why shifting manure to biochar for soil amendment reduces ARG pollution. Thus, this study investigated the variations of ARGs and microbial communities in soil amended with swine manure (2 % and 5 %) and its biochar (2 % and 5 %) and then explored how shifting swine manure to biochar reduced ARG contamination. After 28 d incubation, ARG number in soil without amendment, manure-amended soils, and biochar-amended soils were 47, 112-136, and 43-52, respectively. ARG abundance in soil without amendment, manure-amended soils, and biochar-amended soils were 7.66 × 107, 4.32 × 109 - 1.42 × 1011, and 8.44 × 107-9.67 × 107 copies g-1 dry soil, respectively. Compared to manure-amended soils, its biochar amendments reduced ARG abundance by 2-4 orders of magnitude and ARG number by 70-93 in soil. Besides, manure amendment altered while biochar did not alter bacterial diversity and composition. The changed soil properties and mobile genetic elements (MGEs) could explain the changes in ARGs. Relative to manure amendments, its biochar amendments reduced mobile genetic elements (MGEs), Proteobacteria and Bacteroidetes in soil, which explained the reduced abundance and diversity of ARGs; however, the multidrug-resistance genes harbored in Proteobacteria and Bacteroidetes were still abundant in biochar-amended soil. This study suggests that converting manure to biochar as a soil amendment can help control the spread of manure ARGs.

Integrated organic and inorganic fertilization and reduced irrigation altered prokaryotic microbial community and diversity in different compartments of wheat root zone contributing to improved nitrogen uptake and wheat yield.

The effect of long-term water and integrated fertilization on prokaryotic microorganisms and their regulation for crop nutrient uptake remains unknown. Therefore, the impact of soil water and integrated fertilization after eight years on prokaryotic microbial communities in different compartments of root zone and their association with wheat nitrogen (N) absorption and yield were investigated. The results showed that compared with fertilization treatments (F), water regimes (W) more drastically modulated the prokaryotic microbial community structure and diversity in bulk soil, rhizosphere and endosphere. The increase of irrigation improved the prokaryotic diversity in the rhizosphere and endosphere while decreased the diversity in the bulk soil. Application of organic fertilizers significantly improved soil organic matter (SOM) and nutrient contents, increased rhizosphere and endophytic prokaryotic microbial diversity, and elevated the relative abundance of aerobic ammonia oxidation and nitrification-related functional microorganisms in rhizosphere and endosphere. Increasing irrigation elevated the relative abundance of functional microorganisms related to aerobic ammonia oxidation and nitrification in the rhizosphere and endosphere. Soil water content (SWC) and NH4+-N as well as NO3--N were key predictors of prokaryotic microbial community composition under W and F treatments, respectively. Appropriate application of irrigation and organic fertilizers increased the relative abundance of some beneficial bacteria such as Flavobacterium. Water and fertilization treatments regulated the prokaryotic microbial communities of bulk soil, rhizosphere and endosphere by altering SWC and SOM, and provided evidence for the modulation of prokaryotic microorganisms to promote nitrogen uptake and wheat yield under long-term irrigation and fertilization. Conclusively, the addition of organic manure (50 %) with inorganic fertilizers (50 %) and reduced amount of irrigation (pre-sowing and jointing-period irrigation) decreased the application amount of chemical fertilizers and water, while increased SOM and nutrient content, improved prokaryotic diversity, and changed prokaryotic microbial community structure in the wheat root zone, resulting in enhanced nutrient uptake and wheat yield.

The fate of antibiotic resistance genes and their influential factors during excess sludge composting in a full-scale plant.

The alteration of antibiotic resistance genes (ARGs) during sludge composting has been less studied in a full-scale plant, causing the miss of practical implications for understanding/managing ARGs. Therefore, this study tracked the changes of ARGs and microbial communities in a full-scale plant engaged in excess sludge composting and then explored the key factors regulating ARGs through a series of analyses. After composting, the absolute and relative abundance of ARGs decreased by 91.90% and 66.57%, respectively. Additionally, pathway analysis showed that MGEs, composting physicochemical properties were the most vital factors directly influencing ARGs. Finally, network analysis indicated that Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria were the main hosts of ARGs. Based on these findings, it can be known that full-scale composting could reduce ARGs risk to an extent.