Slope gradient and slope position shape soil microbial communities and antibiotic resistance gene structure in gently sloping arable land

Soil is an important reservoir of ARGs and gently sloping arable land is one of the most important land resources for crop production and food security. The effects of slope gradient and slope position as important variables affecting gently sloping arable soils on ARGs are not well understood. In this study, metagenomics was used to investigate the diversity and abundance of ARGs and bacterial communities in soils of five different slope gradients and two slope positions. High diversity of ARGs (20 ARG types containing 659 subtypes) were identified in all slopes, with multidrug resistance and antibiotic efflux being the predominant resistance class and mechanism respectively, suggesting . 17 bacterial genera were identified as potential ARGs hosts, and 5 soil chemical properties were significantly correlated with soil bacteria communities. SEM analysis further reveals that the main driving factor of ARGs is soil physicochemical properties, while bacterial diversity has a negative effect on ARGs abundance. Our results deepen the understanding of the differences in the distribution structure of ARGs in gentle slope cultivated soil, and emphasize that the types and distribution of ARGs may vary with slope gradient and position.

土壤是抗生素抗性基因（Antibiotic Resistance Genes, ARGs）的重要储存库，缓坡耕地是支撑作物生产与保障粮食安全的核心土地资源之一。坡度与坡位作为影响缓坡耕地土壤的关键环境变量，其对抗生素抗性基因的作用机制尚未得到充分阐释。本研究采用宏基因组学技术，系统探究了5种不同坡度及2种坡位下土壤中抗生素抗性基因的多样性、丰度与细菌群落结构。研究在所有坡度的土壤样本中均检测到多样性极高的抗生素抗性基因，共计包含20类、659个亚型；其中多重耐药类为最主要的抗性类型，抗生素外排机制为最主要的抗性机制。本研究共鉴定出17个潜在的抗生素抗性基因宿主细菌属，且5项土壤化学性质与土壤细菌群落呈显著相关。结构方程模型（Structural Equation Modeling, SEM）分析进一步揭示，土壤理化性质是驱动抗生素抗性基因丰度变化的核心因子，而细菌多样性对抗生素抗性基因丰度存在负向调控作用。本研究结果深化了学界对缓坡耕地土壤中抗生素抗性基因分布结构差异的认知，并强调抗生素抗性基因的类型与分布可能随坡度与坡位的变化而发生改变。