Search

Although the enrichment of antibiotic resistance genes (ARGs) in diverse organic soils have been explored, understanding of the ecological processes governing the composition of ARGs in long-term organically fertilized soils still remains limited across typical agricultural regions. Thus, the distribution and assembly of ARG profile in three typical agricultural soils (black soil, fluvo-aquic soil, and red soil) under long-term contrasting fertilization regimes (chemical-only vs organic-only) were investigated using high-throughput qPCR (HT-qPCR). The application of organic manure significantly increased the abundance and number of ARGs across soils, as compared to those with chemical fertilizer. Organic manure application enriched the abundance of mobile genetic elements (MGEs), which were positively associated with ARGs. In addition, it is long-term organic fertilizer that enriched the number and abundance of opportunist and specialist ARGs in the fluvo-aquic and red soils, but not black soils. The number and abundance of most generalist ARGs did not change significantly among different fertilization or soil types. The assembly process of the ARG profiles tends to be more deterministic in organically fertilized soils than in chemically fertilized soils. These results suggest that long-term organic fertilizer application may contribute to the persistence and health risk of the soil antibiotic resistomes (especially specialist ARGs). [Display omitted] • Animal manures inputs increased the abundance and number of total ARGs in typical agricultural soils. • Opportunist, specialist, and generalist ARGs were identified in the over 30 years of fertilized soils. • Long-term organic fertilizer enriched the number and abundance of opportunist and specialist ARGs. • Deterministic processes mainly shaped ARGs community in organically fertilized soils. [ABSTRACT FROM AUTHOR]

Partial organic fertilizer substitution for chemical fertilizer has been proven to reduce the synthetic nitrogen (N) fertilizer requirement while maintaining or improving rice yield. However, little is known about the underlying physiological mechanisms of such an effect. Field trials were conducted to investigate the effect of organic fertilizer substitution for chemical fertilizer on rice yield and the source – sink relationship in two growing seasons. The treatments were as follows: no N fertilizer application (CK); farmers' fertilizer practice (FFP); optimal chemical N management (OPT); and organic fertilizer substitution based on the OPT treatment (OPT-SN). Compared with treatments of chemical N fertilizer alone, rice yield was maintained in the OPT-SN treatment. The value of the sink – source difference in rice was positive during the grain filling period irrespective of the treatments, implying that the grain yield was source-limited. Although the effects on sink growth were similar among the different N addition treatments, organic fertilizer substitution improved source capacity by extending the duration of source activity when compared with treatments only containing chemical N fertilizer. The source – sink relationship was more balanced (lower sink – source difference) in the OPT-SN treatment relative to treatments of chemical N fertilizer alone, and a significant negative relationship between sink – source difference and grain yield was observed. Overall, organic fertilizer substitution could maintain grain yield by establishing a more balanced source – sink relationship during the grain filling period. Our findings clarify the positive effect of organic fertilizer substitution on source – sink balance and provide a basis for fertilization strategies to improve crop productivity. • Organic substitution extended the duration of source growth. • Organic substitution was beneficial for source capacity. • Organic substitution maintained yield through a balanced source–sink relationship. [ABSTRACT FROM AUTHOR]