Biochar reduces antibiotic transport by altering soil hydrology and enhancing antibiotic sorption.

The performance of biochar (BC) in reducing the transport of antibiotics under field conditions has not been sufficiently explored. In repacked sloping boxes of a calcareous soil, the effects of different BC treatments on the discharge of three relatively weakly sorbing antibiotics (sulfadiazine, sulfamethazine, and florfenicol) via runoff and drainage were monitored for three natural rain events. Surface application of 1 % BC (1 %BC-SA) led to the most effective reduction in runoff discharge of the two sulfonamide antibiotics, which can be partly ascribed to the enhanced water infiltration. The construction of 5 % BC amended permeable reactive wall (5 %BC-PRW) at the lower end of soil box was more effective than the 1 %BC-SA treatment in reducing the leaching of the most weakly sorbing antibiotic (florfenicol), which can be mainly ascribed to the much higher plant available and drainable water contents in the 5 %BC-PRW soil than in the unamended soil. The results of this study highlight the importance of BC's ability to regulate flow pattern by modifying soil hydraulic properties, which can make a significant contribution to the achieved reduction in the transport of antibiotics offsite or to groundwater.

A novel tool for tracing water sources of streamflow in a mixed land-use catchment.

Tracing water sources of streamflow in a mixed land-use catchment is critical for predicting pollutant emissions from various human activities to streams but remains a major challenge. A rain event based field monitoring study was conducted in the Jieliu catchment located in the hilly area of central Sichuan Province, southwest China. The ratio of the maximum fluorescence intensities (Fmax) of the two humic-like dissolved organic matter (DOM) components at excitation/emission wavelengths of 255 (315)/415 nm (component 1; C1) and 260 (375)/480 nm (component 2; C2) was proposed as a tracer for quantifying streamflow water sources. Satisfactory performance of using the Fmax(C1)/Fmax(C2) ratio in hydrograph separation of streamflow at the outlet of a forest sub-catchment was verified by through comparison with the hydrograph separation results based on δ18O data. The Fmax(C1)/Fmax(C2) ratio was then applied to estimate the contributions of rainwater and pre-event water sources under different land use types to the streamflow in an agro-forest sub-catchment and the entire catchment. The hydrograph separation results using the Fmax(C1)/Fmax(C2) ratio can be used to support the optimization of water resource management and the quantification of pollutant loadings from major water sources to streams at the catchment scale.

[Effect of intercropping with Vicia faba on secondary metabolites and rhizosphere soil microbial diversity of Notopterygium incisum].

Rhizosphere soil microbial community and its diversity are important for the structure and functions of medicinal plant ecosystem. In this study, based on high-throughput sequencing, rhizosphere soil microbial diversity, and yield and quality of rhizome and root of Notopterygium incisum cultivated alone(control, CK) and intercropped with Vicia faba(QH) were analyzed, which is expected to lay a basis for optimization of the cultivation mode and ecological production of N. incisum. RESULTS:: showed that the rhizosphere soil bacteria of N. incisum were dominated by Proteobacteria and Bacteroides, with the relative abundance of 50.38%-51.95% and 16.36%-17.02%, respectively. Soil bacterial community at the phylum level was not significantly different between CK and QH. At the genus level, the relative abundance of MND1(3.54%), Spinstomonas(3.50%), Nitrospira(1.53%), and Rhizobacter(1.05%) was significantly higher and that of Gemmatimonas, Candidatus＿Solibacter, and Bryophytes was lower in QH treatment than in the CK. The plant height, leaf length, leaf width, and petiole length of N. incisum in QH treatment was significantly increased and the underground biomass rose by 71.43% compared with those in the CK. Thus, intercropping with V. faba promoted the aboveground growth of N. incisum and improved the yield of root and rhizome. Moreover, the content of notopterol and isoimperatorin increased by 37.96% and 4.09% in QH treatment, respectively, indicating that the intercropping with V. faba boosted the accumulation of secondary metabolites in N. incisum. Pearson's correlation analysis showed that the soil bacterial community was mainly influenced by the soil factors including the content of soil available nutrients, soil organic matter, pH value, and soil water. The influence was in the order: total potassium>total nitrogen>pH>organic matter>available potassium>soil water content>available nitrogen>available phosphorus. In conclusion, the intercropping with V. faba altered soil microenvironment and also increased the yield and accumulation of secondary metabolites of N. incisum, which is a promising ecological planting model for N. incisum.

Distinct aggregate stratification of antibiotic resistome in farmland soil with long-term manure application.

Agricultural soils, which are closely linked to human health via food supply, have been recognized as an important reservoir for antibiotic resistance genes (ARGs). However, there is still a lack of knowledge regarding the role of soil aggregates in shaping ARG profile. In this study, we collected soils from long-term experimental farmland plots receiving inorganic and/or organic fertilizers and examined the patterns of antibiotic resistome distribution among differently sized soil aggregates using high-throughput quantitative polymerase chain reaction (HT-qPCR). Our results showed that the distribution of soil ARGs could be affected by manure application and aggregate size individually but not interactively. More diverse and abundant ARGs were found in the manured soils, compared to the non-manured soils. The aggregate size fraction of <53 µm exhibited the highest diversity and abundance of ARGs. Variation partitioning analysis revealed that soil traits, mobile genetic elements, and bacterial community collectively contributed to the variation of soil antibiotic resistance. The knowledge about aggregation stratification of soil ARGs obtained in this study is fundamental and essential to understanding the fate of soil ARGs at the microscale.

Dynamics and sources of colloids in shallow groundwater in lowland wells and fracture flow in sloping farmland.

Field-scale studies of natural colloid mobilization and transport in finely fractured aquifer as well as the source identification of groundwater colloids are of great importance to the safety of shallow groundwater. In this study, the daily monitoring of fracture flow from a sloping farmland plot and the biweekly monitoring of three lowland shallow wells within the same catchment were carried out simultaneously in 2013. The effects of physicochemical perturbations on groundwater colloid dynamics were explored in detail using partial redundancy analysis, structural equation modeling, Pearson correlation and multi-linear regression analyses. The characterization and source identification of groundwater colloids were addressed via multiple parameters. The daily colloid concentration in the fracture flow varied between 0.54 and 31.90 mg/L (1.64 mg/L on average). Unique periods of high colloid concentration (5.59 mg/L on average) occurred during the initially generated flow following the dry season. In comparison, a narrower colloid concentration range of 0.24-11.66 mg/L was observed in the lowland shallow wells, with a smaller temporal variation than that of the fracture flow. A low percentage (2.4-7.0%) of colloids and a high percentage (47.7-92.0%) of coarse particles (2-10 µm) were present in the lowland well water. Hydraulic perturbation by rainwater infiltration in the sloping farmland was the dominant mechanism for colloid mobilization in general; this effect retreated to secondary importance behind chemical perturbations (pH, Mg2+ and DOC) at low flow discharges (<1.3 L/min). In contrast, water chemistry (e.g., EC, cations and DOC concentrations) exhibited a major effect on colloid dynamics in the water of the lowland wells, except for the extremely high-salinity water of one well, in which water temperature showed a negative dominant influence on colloid stability. The combined use of multiple parameters (e.g., mineral composition and organic matter, calcium carbonate and δ13C contents) traced groundwater colloids to the shallow soil in the upper farmlands. It is strongly advised that in finely fractured aquifers within agricultural catchments, not only the small colloids but also the coarse particles in the size range of 2-10 µm should be monitored in case of colloid-associated contamination from agricultural wastes e.g., N, P, pesticides and/or heavy metals, especially at the early stages of the rainy seasons.

Effect of long-term manure slurry application on the occurrence of antibiotic resistance genes in arable purple soil (entisol).

The application of animal manure is a highly recommended traditional agricultural practice for soils of relatively low fertility. However, for the farmland purple soils that are widely distributed in the upper Yangtze River region, little knowledge has been established in previous studies about the changes in the antibiotic resistome upon manure amendment. In the present study, the impact of long-term pig manure slurry application on the occurrence of antibiotic resistance genes (ARGs) and bacterial community was assessed in arable calcareous purple soil using high-throughput quantitative polymerase chain reaction and Illumina sequencing. Four treatments, including a non-fertilization control (CK) and pig manure (OM), OM plus mineral N fertilizer (OMN) and OM plus mineral NPK fertilizer (OMNPK) treatments were investigated. Across all the soil samples receiving different treatments, a total of 139 unique ARGs and 6 mobile genetic element genes were detected, with multidrug and beta-lactam the two most dominant types of ARGs. The results of the principal coordinate analysis (PCoA) suggest that the profiles of soil ARGs in the two treatments of OM combined with mineral fertilizer(s) (i.e., OMN and OMNPK) were similar to those in the control treatment, while the soil receiving only pig manure application had a different pattern of ARGs from the soils in the other three treatments. A clear reduction of soil ARGs was observed in the OM treatment. Significant and positive relationships were found not only among ARGs but also between mobile genetic elements (MGEs) and ARGs. However, no significant relationships were detected between ARG patterns and bacterial community composition. These results imply that the long-term application of pig manure slurry to purple soil does not lead to the prevalence of ARGs; however, the potential for the horizontal transfer of ARGs in calcareous purple soil should not be ignored.