Agricultural land-use change exacerbates the dissemination of antibiotic resistance genes via surface runoffs in Lake Tai Basin, China.

Agricultural runoff is an important antibiotic resistance genes (ARGs) dissemination pathway from farmlands to water environment, however few studies have focused on the influence of agricultural land-use change on the pattern of ARGs in runoff and assess the health risk to public. Lake Tai Basin which experiences agricultural land-use change was selected to elucidate this concern. Our findings revealed that the pattern of ARGs was more diverse and the gene abundance was higher in orchard runoffs by comparison with conventional cropland runoffs. Co-occurrence network analysis between mobile genetic elements and ARGs demonstrated that after agricultural land-use change, ARG dissemination via runoffs became more threatened. In addition, this study illustrated the correlations between the antibiotic resistome and microbiome in runoffs, finding that non-dominant microbial taxa were the limiting factor which determined the pattern of ARGs in surface runoffs. In summary, the pattern and dissemination risk of ARGs in the surface runoff after agricultural land-use change in Lake Tai Basin were clarified via this study.

Agricultural land-use change and rotation system exert considerable influences on the soil antibiotic resistome in Lake Tai Basin.

In this study, we use high-throughput quantitative polymerase chain reaction approaches to comprehensively assess the effects of agricultural land-use change on the antibiotic resistome of agricultural runoffs after rainfalls in Lake Tai Basin. For the first time in this region, our findings show that orchard runoffs harbored more diverse and abundant antibiotic resistance genes (ARGs) than traditional cropland runoffs. Network analysis demonstrated that orchard runoffs possessed a strong ability for ARG dissemination via horizontal gene transfer. These results suggest that residents might be exposed to a higher public health threat than before. Moreover, the present study confirmed that the rice-wheat rotation system plays a key role in regulating the soil antibiotic resistome profile. Using 16S rRNA high-throughput sequencing technology, this study clarified the relationships between the antibiotic resistome and soil microbiome composition. Finally, we discuss the key environmental factors driving changes in the soil antibiotic resistome. In summary, this study gives insight into the dissemination of environmental ARGs to the people living in the Lake Tai Basin.

Influence of elevated CO2 on nitrification and denitrification in water bodies: A review.

Elevated atmospheric CO2 has imperceptible impacts on carbon cycle in aquatic ecosystems. However, it remains a question how this process will impact nitrogen cycle that is naturally coupled with carbon cycle. The nitrification and denitrification are two critical processes in the nitrogen cycle. It is reasonable to expect that elevated atmospheric CO2 will influence both processes. We reviewed the previous literatures concerning the effects of elevated atmospheric CO2 on the physico-chemical properties, nitrification, denitrification and nitrogen transformation in water bodies. The published results revealed that the elevated CO2 would reduce the water pH, increase CO2 and HCO3- concentrations, but with different effects on the nitrification and denitrification between eutrophic and oligotrophic water. Elevated atmospheric CO2 could inhibit nitrification and denitrification in oligotrophic water, thereby reduce N2O flux from water. The nitrification process in the eutrophic water bodies was also inhibited, but its denitrification might be promoted by the elevated CO2. In the eutrophic water bodies, there could be an increase of N2O flux when pH was maintained in the range of 7-9. These might eventually result in the accumulation of NH4+ and reduction of NO3- in water, producing an impact on the microbial diversity. Based on these reviews, we proposed some research gaps related to the relevant research fields as well as some scientific questions that is worth to be further explored. This review would be helpful to better understanding on how the greenhouse effect caused by the elevated atmospheric CO2 would affect nitrogen cycle in aquatic ecosystem.