Long-term excessive fertilization and irrigation under greenhouse cultivation systems cause nitrogen leaching, while the residual content varies at different soil depths with cultivation durations. However, it remains unclear whether it changes the composition and assemblage of the soil bacterial community, especially at deeper layers (as deep as 4 m), after long-term intensified cultivation. This study selected soils from three sites in Shouguang (a typical representative intensive planting area), i.e., greenhouse monoculturing for 20 years (G20), greenhouse monoculturing for 10 years (G10), and an adjacent rotation field (F) for physicochemical property determination and high-throughput pyrosequencing. The results showed that, contrary to the vertical characterization of soil bacterial community composition, the 2-m soil was dominated by Methylomirabilota, a nitrate/nitrite-dependent anaerobic methane oxidizer, uncovered for the first time in the soil habitat. This was attributed to the high levels of dissolved organic carbon (DOC, 201.2–255.7 mg kg−1), proving that applying C-rich organic fertilizers, e.g. plant residues, is effective in preventing accumulated nitrate from moving downward and threatening groundwater in greenhouse soils. Besides, greenhouse cultivation increased the inter-layer composition differences of the bacterial community, and compared with the abundant, the rare subcommunity showed higher sensitivity to environmental changes. The total nitrogen most significantly affected the bacterial community composition and assemblage. Therefore, 20 years of consecutive monocropping significantly decreased the microbial co-occurrence network complexity and species dispersal rate, yielding a low-fitted neutral community model (NCM) and more specialized ecological niches, especially for the rare subcommunity. As far as is known, this is the first study that explores the likely changes in the bacterial community composition and quantifies the responses of the rare subcommunity to long-term greenhouse cultivation at this soil depth. Discovery of Methylomirabilota broadens our understanding of micro-biodiversity in deep-soil ecosystem, and hints its application potential in soil remediation.

中文翻译：

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深入挖掘发现长期温室栽培和过度施肥灌溉对土壤细菌群落结构和组装的影响


温室栽培系统下长期过度施肥和灌溉会导致氮素淋失，而不同土壤深度的残留含量随栽培时间的变化而变化。然而，目前尚不清楚在长期集约化培养后，它是否会改变土壤细菌群落的组成和组合，尤其是在更深的层（深达 4 m）处。本研究从寿光市典型的代表性集约化种植区3个地点选取土壤，即温室单作20年生（G20）、温室单作10年生（G10）和相邻轮换田（F）进行理化性质测定和高通量焦磷酸测序。结果表明，与土壤细菌群落组成的垂直特征相反，2 m 土壤以 Methylomirabilota（一种硝酸盐/亚硝酸盐依赖性厌氧甲烷氧化剂）为主，首次在土壤生境中发现。这归因于高水平的溶解有机碳（DOC，201.2-255.7 mg kg-1），证明施用富含碳的有机肥料，例如植物残留物，可有效防止积累的硝酸盐向下移动并威胁温室土壤中的地下水。此外，温室栽培增加了细菌群落的层间组成差异，与丰富相比，稀有亚群落对环境变化表现出更高的敏感性。总氮对细菌群落组成和组装的影响最显着。 因此，连续 20 年的单一种植显著降低了微生物共生网络复杂性和物种扩散率，产生了低拟合中性群落模型 （NCM） 和更专业化的生态位，尤其是稀有亚群落。据了解，这是第一项探索细菌群落组成可能变化并量化稀有亚群落对该土壤深度长期温室栽培的反应的研究。Methylomirabilota 的发现拓宽了我们对深层土壤生态系统中微生物多样性的理解，并暗示了其在土壤修复中的应用潜力。