Impact of residual antibiotics on microbial decomposition of livestock manures in Eutric Regosol: Implications for sustainable nutrient recycling and soil carbon sequestration.

The land application of livestock manure has been widely acknowledged as a beneficial approach for nutrient recycling and environmental protection. However, the impact of residual antibiotics, a common contaminant of manure, on the degradation of organic compounds and nutrient release in Eutric Regosol is not well understood. Here, we studied, how oxytetracycline (OTC) and ciprofloxacin (CIP) affect the decomposition, microbial community structure, extracellular enzyme activities and nutrient release from cattle and pig manure using litterbag incubation experiments. Results showed that OTC and CIP greatly inhibited livestock manure decomposition, causing a decreased rate of carbon (28%-87%), nitrogen (15%-44%) and phosphorus (26%-43%) release. The relative abundance of gram-negative (G-) bacteria was reduced by 4.0%-13% while fungi increased by 7.0%-71% during a 28-day incubation period. Co-occurrence network analysis showed that antibiotic exposure disrupted microbial interactions, particularly among G- bacteria, G+ bacteria, and actinomycetes. These changes in microbial community structure and function resulted in decreased activity of urease, ß-1,4-N-acetyl-glucosaminidase, alkaline protease, chitinase, and catalase, causing reduced decomposition and nutrient release in cattle and pig manures. These findings advance our understanding of decomposition and nutrient recycling from manure-contaminated antibiotics, which will help facilitate sustainable agricultural production and soil carbon sequestration.

Selective increase of antibiotic-resistant denitrifiers drives N2O production in ciprofloxacin-contaminated soils.

Agricultural systems significantly contribute to global N2O emissions, which is intensified by excessive fertilization and antibiotic residues, attracting global concerns. However, the dynamics and pathways of antibiotics-induced soil N2O production coupled with microbial metabolism remain controversial. Here, we explored the pathways of N2O production in agricultural soils exposed to ciprofloxacin (CIP), and revealed the underlying mechanisms of CIP degradation and the associated microbial metabolisms using 15N-isotope labeling and molecular techniques. CIP exposure significantly increases the total soil N2O production rate. This is attributed to an unexpected shift from heterotrophic and autotrophic nitrification to denitrification and an increased abundance of denitrifiers Methylobacillus members under CIP exposure. The most striking strain M. flagellatus KT is further discovered to harbor N2O-producing genes but lacks a N2O-reducing gene, thereby stimulating denitrification-based N2O production. Moreover, this denitrifying strain is probably capable of utilizing the byproducts of CIP as carbon sources, evidenced by genes associated with CIP resistance and degradation. Molecular docking further shows that CIP is well ordered in the catalytic active site of CotA laccase, thus affirming the potential for this strain to degrade CIP. These findings advance the mechanistic insights into N2O production within terrestrial ecosystems coupled with the organic contaminants degradation.

Reducing carbon and nitrogen loss by shortening the composting duration based on seed germination index (SCD@GI): Feasibilities and challenges.

Addressing carbon (C) and nitrogen (N) losses through composting has emerged as a critical environmental challenge recently, and how to mitigate these losses has been a hot topic across the world. As the emissions of carbonaceous and nitrogenous gases were closely correlated with the composting process, the feasibility of composting duration shortening on C and N loss needs to be explored. Therefore, the goal of this paper is to find evidence-based approaches to reduce composting duration, utilizing the seed germination index as a metric (SCD@GI), for assessing its efficiency on C and N loss reductions as well as compost quality. Our findings reveal that the terminal seed germination index (GI) frequently surpassed the necessary benchmarks, with a significant portion of trials achieving the necessary GI within 60 % of the standard duration. Notably, an SCD@GI of 80 % resulted in a reduction of CO2 and NH3 by 21.4 % and 21.9 %, respectively, surpassing the effectiveness of the majority of current mitigation strategies. Furthermore, compost quality, maturity specifically, remained substantially unaffected at a GI of 80 %, with the composting process maintaining adequate thermophilic conditions to ensure hygienic quality and maturity. This study also highlighted the need for further studies, including the establishment of uniform GI testing standards and comprehensive life cycle analyses for integrated composting and land application practices. The insights gained from this study would offer new avenues for enhancing C and N retention during composting, contributing to the advancement of high-quality compost production within the framework of sustainable agriculture.

Co-benefits for net carbon emissions and rice yields through improved management of organic nitrogen and water.

Returning organic nutrient sources (for example, straw and manure) to rice fields is inevitable for coupling crop-livestock production. However, an accurate estimate of net carbon (C) emissions and strategies to mitigate the abundant methane (CH4) emission from rice fields supplied with organic sources remain unclear. Here, using machine learning and a global dataset, we scaled the field findings up to worldwide rice fields to reconcile rice yields and net C emissions. An optimal organic nitrogen (N) management was developed considering total N input, type of organic N source and organic N proportion. A combination of optimal organic N management with intermittent flooding achieved a 21% reduction in net global warming potential and a 9% rise in global rice production compared with the business-as-usual scenario. Our study provides a solution for recycling organic N sources towards a more productive, carbon-neutral and sustainable rice-livestock production system on a global scale.

A comprehensive and global evaluation of residual antibiotics in agricultural soils: Accumulation, potential ecological risks, and attenuation strategies.

The occurrence of antibiotics in agricultural soils has raised concerns due to their potential risks to ecosystems and human health. However, a comprehensive understanding of antibiotic accumulation, distribution, and potential risks to terrestrial ecosystems on a global scale is still limited. Therefore, in this study, we evaluated the accumulation of antibiotics and their potential risks to soil microorganisms and plants, and highlighted the driving factors of antibiotic accumulation in agricultural soils based on 134 peer-reviewed studies (between 2000 and 2022). The results indicated that 56 types of antibiotics were detected at least once in agricultural soils with concentrations ranging from undetectable to over 7000 µg/kg. Doxycycline, tylosin, sulfamethoxazole, and enrofloxacin, belonging to the tetracyclines, macrolides, sulfonamides, and fluoroquinolones, respectively, were the most accumulated antibiotics in agricultural soil. The accumulation of TCs, SAs, and FQs was found to pose greater risks to soil microorganisms (average at 29.3%, 15.4%, and 21.8%) and plants (42.4%, 26.0%, and 38.7%) than other antibiotics. East China was identified as a hot spot for antibiotic contamination due to high levels of antibiotic concentration and ecological risk to soil microorganisms and plants. Antibiotic accumulation was found to be higher in vegetable fields (245.5 µg/kg) and orchards (212.4 µg/kg) compared to croplands (137.2 µg/kg). Furthermore, direct land application of manure resulted in a greater accumulation of TCs, SAs, and FQs accumulation in soils than compost fertilization. The level of antibiotics decreased with increasing soil pH and organic matter content, attributed to decreasing adsorption and enhancing degradation of antibiotics. In conclusion, this study highlights the need for further research on the impacts of antibiotics on soil ecological function in agricultural fields and their interaction mechanisms. Additionally, a whole-chain approach, consisting of antibiotic consumption reduction, manure management strategies, and remediation technology for soil contaminated with antibiotics, is needed to eliminate the potential environmental risks of antibiotics for sustainable and green agriculture.

Occurrence profiling and environmental risk assessment of veterinary antibiotics in vegetable soils at Chongqing region, China.

Veterinary antibiotics (VAs) are emerging contaminants in soils as they may pose high risks to the ecosystem and human health. Identifying VAs accumulation in soils is essential for assessing their potential risks. Therefore, we investigated the distribution of VAs in soils from vegetable fields and evaluated their potential ecological and antimicrobial resistance risks in the Chongqing region of the Three Gorges Reservoir area, China. Results indicated that twenty-six species of VAs, including nine sulfonamides (SAs), seven quinolones (QNs), four tetracyclines (TCs), four macrolides (MLs), and two other species of VAs were detected in soils, with their accumulative levels ranging from 1.4 to 3145.7 µg kg-1. TCs and QNs were the dominant VAs species in soils with high detection frequencies (100% TCs and 80.6% for QNs) and accumulative concentration (up to 1195 µg kg-1 for TCs and up to 485 µg kg-1 for QNs). Risk assessment indices showed that VAs (specifically SAs, TCs, and QNs) in most vegetable soils would pose a medium to high risk to the ecosystem and antimicrobial resistance. Mixture of VAs posed a higher risk to soil organisms, antimicrobial resistance, and plants than to aquatic organisms. Modeling analysis indicated that socioeconomic conditions, farmers' education levels, agricultural practices, and soil properties were the main factors governing VAs accumulation and environmental risks. Farmers with a high educational level owned large-scale farms and were more willing to use organic fertilizers for vegetable production, which eventually led to high VAs accumulation in vegetable soil. These findings would provide a reference for sustainable agricultural and environmental production under the current scenario of chemical fertilizer substitution by organic products and green agricultural development.

[Pollution Characteristics and Source Apportionment of Heavy Metals in Vegetable Field in the Three Gorges Reservoir Area (Chongqing Section)].

To explore the pollution characteristics, ecological risks, and sources of heavy metals, soil surface samples of vegetable fields in 14 typical districts of the Three Gorges Reservoir area (Chongqing section) were collected in October 2021. The contents of seven types of heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were analyzed. Based on the single-factor pollution index, the Nemerow integrated pollution index and potential ecological risk coefficient of heavy metals were evaluated. Additionally, the effects of different planting years and methods (open-field and greenhouse planting) on soil heavy metal accumulation were analyzed. The results indicated that the mean concentrations of heavy metals in vegetable soils in the area were lower than the national risk screening values for soil contamination of agricultural land (GB 15618-2018) but higher than their background values in Chongqing. According to the single-factor pollution index method, Pb, Zn, Cu, and Cd showed negligible slight hazards. The Nemerow pollution index showed that the study area was at a slight hazard level, and the main factors were Ni and Cd. Heavy metal pollution was found in 91.4% of the soil samples (PN>1) with different degrees, and 9.19% of them were severely polluted. The potential ecological risk coefficient showed that the vegetable lands were polluted slightly, and 9.77% of soil samples polluted by Cd were at moderate ecological risk. According to cluster analysis, the sources of Cd-Cu-Pb-Zn and As-Cr-Ni were similar. The content of heavy metals in the open field and greenhouse showed an increasing trend with the increase in planting years, and the content of heavy metals in greenhouse soil were generally higher than that in open field soil.

Insights into carbon loss reduction during aerobic composting of organic solid waste: A meta-analysis and comprehensive literature review.

Carbon neutrality is now receiving global concerns for the sustainable development of human societies, of which how to reduce greenhouse gases (GHGs) emissions and enhance carbon conservation and sequestration becomes increasingly critical. Therefore, this study conducted a meta-analysis and literature review to assess carbon loss and to explore the main factors that impact carbon loss during organic solid waste (OSW) composting. The results indicated that over 40 % of carbon was lost through composting, mainly as CO2-C and merely as CH4-C. Experimental scale, feedstock varieties, composting systems, etc., all impacted the carbon loss, and there was generally higher carbon loss under optimal conditions (i.e., C/N ratio (15-25), pH (6.5-7.5), moisture content (65-75 %)). Most mitigation strategies in conventional composting (CC) systems (e.g., additive supplementary, feedstock adjustment, and optimized aeration, etc.) barely mediated the TC and CO2-C loss but dramatically reduced the emission of CH4-C through composting. Among them, feedstock adjustment by elevating the feedstock C/N ratio effectively reduced the TC loss, and chemical additives facilitated the conservation of both carbon and nitrogen. By comparison, there was generally higher carbon loss in the novel composting systems (e.g. hyperthermophilic and electric field enhanced composting, etc.). However, the impacts of different mitigation strategies and novel composting systems on carbon loss reduction through composting were probably underestimated for the inappropriate evaluation methods (composting period-dependent instead of maturity originated). Therefore, further studies are needed to explore carbon transformation through composting, to establish methods and standards for carbon loss evaluation, and to develop novel techniques and systems for enhanced carbon conservation through composting. Overall, the results of this study could provide a reference for carbon-friendly composting for future OSW management under the background of global carbon neutrality.

[Pollution Characteristics and Ecological Risk Assessment of Antibiotics in Vegetable Field in Kaizhou, Chongqing].

The accumulation of antibiotics in farmland and its ecological risk have become a research hotspot at home and abroad. The objective of this study was to investigate the occurrence and accumulation of antibiotics and their potential environmental and ecological risks in vegetable fields in Kaizhou district of Chongqing country. The occurrence characteristics of antibiotics including tetracyclines, sulfonamides, quinolones, macrolides, and chloramphenicols were detected using experimental analysis. The results showed that there was an accumulation of antibiotics in the vegetable soil, and 18 antibiotics in five categories were detected (0-42.88 µg·kg-1), mainly for tetracyclines and quinolones. The detection rate of quinolone antibiotics was the highest (15.38%-100%), especially for norfloxacin and ofloxacin (100%), whereas the tetracyclines presented the highest concentration (0-42.88 µg·kg-1). The amount of total antibiotics in the vegetable soil was 1.64-233.11 µg·kg-1, whereas different vegetable soils showed the following trend:water spinach soil (89.73 µg·kg-1)>cabbage soil (32.53 µg·kg-1)>pepper soil (32.16 µg·kg-1)>tomato soil (32.13 µg·kg-1)>cucumber soil (26.46 µg·kg-1)>grassland (7.32 µg·kg-1). The correlation results showed that there was a significantly positive correlation between total antibiotic residues and organic fertilizer application (P<0.05) but a significantly negative correlation with soil pH (P<0.05). Quinolones and sulfonamides were negatively correlated with soil water content (P<0.05), whereas quinolones positively correlated with soil available phosphorus and organic matter content (P<0.05). The potential eco-environmental risk assessment results showed that tetracyclines and quinolones in vegetable soil in Kaizhou district had certain ecological risks, of which 62%-92% and 62%-100% of soil samples with quinolones had potential toxicity to soil animals and microorganisms.