摘要
      改良源自牲畜粪便或生物固体的有机肥料是增加农业土壤抗生素耐药性的重要驱动因素；然而，目前尚不清楚增加有机肥施用量是否会持续提高土壤抗生素耐药性水平。在此，我们收集了用三种类型的有机肥料以四种施用率（15、30、45和60t/ha/y）长期改良的土壤，发现施肥率越高，抗生素抗性基因（ARG）的丰度就越高。然而，当施肥量超过45t/ha/y时，ARG丰度停止显著增加。此外，土壤ARG丰度与总氮（TN）含量和细菌丰度呈正相关，尤其是厚壁菌门，而与pH和细菌多样性呈负相关。土壤TN/细菌丰度和pH/细菌多样性在45t/ha/y施肥率下分别达到最大值和最小值。同时，在这个受精率下，厚壁菌门的富集达到峰值。因此，在本研究中，45t/ha/y的有机施肥率似乎代表了土壤抗生素耐药性的阈值。该阈值的潜在机制与土壤总氮、pH、细菌丰度和多样性密切相关。总之，这项研究的发现促进了目前对不同施肥率下土壤抗性的理解，同时也为农业实践中的有机肥料管理提供了新的见解。
Abstract
The amendment of organic fertilizer derived from livestock manure or biosolids is a significant driver of increasing antibiotic resistance in agricultural soils; however, it remains unclear whether increasing organic fertilizer application rates consistently enhances soil antibiotic resistance levels. Herein, we collected soils with long-term amendment with three types of organic fertilizers at four application rates (15, 30, 45, and 60 t/ha/y) and found that the higher the fertilization rate, the higher the antibiotic resistance gene (ARG) abundance. However, when the fertilization rate exceeded 45 t/ha/y, the ARG abundance ceased to significantly increase. Moreover, the soil ARG abundance was positively correlated with total nitrogen (TN) content and bacterial abundance, especially Firmicutes, and negatively affected by pH and bacterial diversity. Soil TN/bacterial abundance and pH/bacterial diversity reached maximum and minimum values at the 45 t/ha/y fertilization rate, respectively. Meanwhile, at this fertilization rate, Firmicutes enrichment peaked. Therefore, an organic fertilization rate of 45 t/ha/y appeared to represent the threshold for soil antibiotic resistance in this study. The underlying mechanism for this threshold was closely related to soil TN, pH, bacterial abundance, and diversity. Taken together, the findings of this study advance the current understanding regarding the soil resistome under different fertilization rates, while also providing novel insights into organic fertilizer management in agricultural practices.

https://www.sciencedirect.com/science/article/abs/pii/S0269749123002531