Leaching of antibiotic resistance genes and microbial assemblages following poultry litter applications in karst and non-karst landscapes

Poultry litter as a soil amendment enriches antibiotic resistant enterococci

While raw poultry litter from broiler houses is used as organic fertilizer for crop production, it may also enrich antibiotic resistant bacteria in the soil. In a randomized field trial, we evaluated the impact of poultry litter as a soil amendment on antimicrobial resistant enterococci in corn fields. Two winter cropping systems (fallow, and cover crop) were assigned to whole plots while three spring applied fertilizer treatments (untreated control, poultry litter, and chemical fertilizer) were randomly assigned to subplots. Soil samples were collected from the top 15 cm on days 0 (baseline, May 1), 7 (May 15), 28 (June 6), 70 (July 17), 98 (August 14), and 172 (October 27) post treatment (pt) in 2017. Samples were cultured for the enumeration and detection of generic (with no antibiotics), erythromycin- (ERYr), and tetracycline-resistant (TETr) enterococci. Resistant subpopulations were characterized for phenotypic and genotypic resistance. Poultry litter amendment significantly (P < 0.05) increased the levels of generic-, ERYr-, and TETr-enterococci on days 7 and 28 pt, compared to untreated control or chemical fertilizer. Beyond d 28 pt, enterococci levels, regardless of resistance status, did not significantly (P > 0.05) differ by fertilizer treatment, and returned to the baseline by d 70 pt. Cover crop significantly increased the concentration of generic enterococci, with no significant effects on the resistant subpopulations. Poultry litter amendment enriched ERYrEnterococcus casseliflavus while the most clinically important species, E. faecalis, was readily detected, regardless of fertilizer treatment. ERY and TET resistance were conferred mainly by ermB and tetM genes, respectively. Raw poultry litter amendment enriches total and antimicrobial resistant enterococci populations in the soil temporarily. However, further studies are needed to elucidate mechanisms behind this reduction after a temporary increase at the site of poultry litter application, and its impact beyond the agronomic fields.

Reuse of wastewater and biosolids in soil conditioning: Potentialities, contamination, technologies for wastewater pre-treatment and opportunities for land restoration

This study reviews the potential use of various wastewaters-vinasse, swine, food industry, paper and pulp, municipal wastewaters, and biosolids-as soil conditioners for restoring degraded areas, focusing on the circular economy concept. Over 90 articles from 2013 to 2024 were analyzed to address current scientific concerns, including these effluents' resistance genes, hormones, and macro/micronutrients. The presence of contaminants was critically examined alongside the necessary treatment methods to prevent soil degradation and ensure soil quality improvement. These included contaminants of emerging concern (CECs), antibiotic resistance genes (AGRs), and pathogens. These contaminants can either be assimilated and degraded by the soil ecosystem or leach into groundwater, translocate to plants, or accumulate in surface soil, necessitating careful monitoring. Furthermore, the study critically evaluates the potential of various physical and biological treatment technologies, such as anaerobic digestion, composting, dewatering, stabilization ponds, biological reactors, membrane processes, rotating disks, and pelletizers, highlighting their effectiveness in mitigating contamination and enhancing soil quality. The long-term effects of wastewater reuse as soil conditioner depend on both wastewater characteristics and soil properties. The benefits of using wastewater as soil conditioners are found to be influenced by characteristics of both the soil and the wastewater, with improvements in soil physical properties (increased porosity and permeability) and chemical properties (increased soil organic carbon and nutrients). Overall, the literature suggests that while wastewaters hold promise as soil conditioners, their successful application depends on effective wastewater management strategies to optimize benefits and mitigate risks.

The past and future dynamics of ecological resilience and its spatial response analysis to natural and anthropogenic factors in Southwest China with typical Karst

With the global land use/land cover (LULC) and climate change, the ecological resilience (ER) in typical Karst areas has become the focus of attention. Its future development trend and its spatial response to natural and anthropogenic factors are crucial for understanding the changes of ecologically fragile areas to human behavior. However, there is still a lack of relevant quantitative research. The study systematically analyzed the characteristics of LULC changes in Southwest China with typical Karst over the past 20 years. Drawing on the landscape ecology research paradigm, a potential-elasticity-stability ER assessment model was constructed. Revealing the characteristics and heterogeneity of the spatial distribution, annual evolution, and development trend of ER in the past and under different scenarios of shared socioeconomic pathways and representative concentration pathways (SSP-RCP) in the future. In addition, the spatial econometric model was utilized to reveal the spatial effect response mechanism of ER, and adaptive development strategies were proposed to promote the sustainable development of Southwest China. The study found that : (1) In the past 20 years, the LULC in Southwest China showed an accelerated change trend, the ER decreased declined in general, and there was significant spatial heterogeneity, showing the spatial distribution pattern of "west is larger than east, south is larger than north, and reduction in the west was slower than that in the east." (2) Under the same SSP scenario, with the increase of RCP emission concentration, the area of the lowest-resilience increased significantly, and the area of the highest-resilience decreased. (3) The woodland was the largest contributor to ER per unit area in the Southwest China, and grassland was the main LULC type, which had a prominent impact on the ER of the study area. (4) The average precipitation and the normalized difference vegetation index (NDVI) were significant natural drivers of ER in the study area, and the economic growth, innovation, and optimization of industrial structure contributed to the ER of Southwest China. Overall, the integration of quantitative assessment and multi-scenario-based modeling not only provides new perspectives for understanding the pattern of change and response mechanisms, but also provides valuable references for other typical Karst regions around the world to achieve sustainable development.