Understanding the processes guiding microbial community assembly in soils is essential for predicting microbiome structure and function following soil disturbance events like agricultural soil fumigation. However, assembly outcomes are complex and variable, being affected by both selective abiotic forces and by the history of colonizing microorganisms. To untangle the interactions between these factors, we conducted a controlled microcosm study tracking bacterial assembly in cleared soils over 7 weeks. We used mesh bags to connect five unsterilized source soils, differing in land use history (forested, agricultural, or fallow), with four sterile recipient soil treatments, differing in abiotic conditions (no soil additives, salt addition, urea addition, or mixed salt/urea addition). We found that 59%–96% of bacterial colonizers after 1 week were Firmicutes, but by 7 weeks Actinobacteria and Bacteroidetes were also dominant. Salt and nitrogen additions reshaped bacterial assembly by constraining alpha diversity by up to half and biomass accumulation by up to an order of magnitude. Within‐treatment dispersion was significantly lower for salt and nutrient addition microcosms, suggesting deterministic selective pressures. In contrast, source soil origin had little impact on assembly trajectories. These results suggest that abiotic conditions can overshadow microbial source history in shaping community assembly outcomes.

中文翻译：

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在土壤中细菌装配过程中，非生物条件胜过微生物来源

了解指导土壤中微生物群落组装的过程对于预测土壤扰动事件（如农业土壤熏蒸）后的微生物组结构和功能至关重要。然而，组装结果是复杂且可变的，受选择性非生物力和微生物定殖历史的影响。为了弄清这些因素之间的相互作用，我们进行了一项受控的微观研究，跟踪了7周内在清洁土壤中细菌的组装情况。我们使用网眼袋将五种未经消毒的原始土壤（土地使用历史不同（森林，农业或休耕））与四种无菌的接受土壤处理方法连接在一起，在非生物条件下（无土壤添加剂，添加盐，添加尿素或混合盐） /脲）。我们发现1周后有59％–96％的细菌菌落是坚定，但到7周时放线菌和拟杆菌也占主导地位。盐和氮的添加通过最多限制一半的α多样性和最多一个数量级的生物量积累来重塑细菌的装配。对于盐和营养物添加的微观世界，处理内分散明显较低，表明确定性的选择压力。相反，源土的来源对装配轨迹几乎没有影响。这些结果表明，非生物条件会在塑造社区集会结果时掩盖微生物来源的历史。