Soil aggregates support diverse microbes due to heterogeneous micro-environment. A lot of researches have exhibited the difference of microbial composition and activity within different size soil aggregates, but the relative influences of these microbes and the mechanisms underlying their effects on plant health are still poorly understood. This study investigated the microbiomes within four soil aggregate fractions sampled from fields with different incidences of tomato bacterial wilt derived from three fertilization regimes (organic, bio-organic and chemical) and un-fertilized soil to decipher the mechanisms involved in disease suppression. A wet-sieving method was used to separate the aggregate fractions; Illumina MiSeq sequencing was used to characterize the soil microbiomes in field experiment, and real-time qPCR analysis was used in lab cultivation experiment to quantify the number of pathogens. Organic fertilization (OF) and bio-organic fertilization (BF) significantly decreased disease incidences compared with the effects of treatments with chemical fertilizer (CF) and those without fertilizer (CK). The microbial composition was significantly different between fertilizations and aggregate fractions; particularly, the bacterial composition was significantly correlated with disease incidence. Different aggregate fractions contained disparate bacterial taxa correlated with disease incidence. Only in the microaggregate (Mi), the Ralstonia genus’ relative abundance showed a significant and positive correlation with disease incidence. The lab cultivation experiment demonstrated that after a spiking of Ralstonia solanacearum , whole soil and the Mi from BF-treated soil showed a significant higher resistance against pathogen invasion than those from CF-treated soil. The correlation between pathogen abundance and disease incidence in the field experiment and the higher resistance of Mi fraction against pathogen indicates that the microaggregates are the key fraction for suppressing tomato bacterial wilt in bio-organic fertilization practice, providing novel insight into the manipulation of the soil microbiome.

中文翻译：

---

生物肥料应用引发与番茄青枯病抑制相关的微团聚体中的微生物组装

由于异质微环境，土壤团聚体支持多种微生物。大量研究表明，不同大小土壤团聚体中微生物组成和活性存在差异，但这些微生物的相对影响及其对植物健康影响的机制仍知之甚少。本研究调查了从三种施肥方式（有机、生物有机和化学）和未施肥的土壤中番茄青枯病发生率不同的田地取样的四种土壤团聚体部分中的微生物组，以破译疾病抑制所涉及的机制。湿筛分法用于分离骨料部分；Illumina MiSeq 测序用于表征田间试验中的土壤微生物组，在实验室培养实验中使用实时qPCR分析来量化病原体的数量。与化肥（CF）和不施肥（CK）处理的效果相比，有机施肥（OF）和生物有机肥（BF）显着降低了病害发生率。施肥和骨料部分的微生物组成存在显着差异；特别是，细菌组成与发病率显着相关。不同的聚集部分包含与疾病发生率相关的不同细菌分类群。仅在微团聚体（Mi）中，Ralstonia 属的相对丰度与发病率呈显着正相关。实验室栽培实验表明，青枯病菌加标后，全土和 BF 处理土壤的 Mi 对病原体入侵的抵抗力显着高于 CF 处理土壤。田间试验中病原体丰度与发病率之间的相关性以及Mi组分对病原体的较高抗性表明微团聚体是生物有机施肥实践中抑制番茄青枯病的关键组分，为土壤操作提供了新的见解微生物组。