Humic acids (HA) stimulate the growth of several plant species by regulating their hormonal and redox metabolisms. Nevertheless, studies on their relationship with the plant-associated microbiota are almost nonexistent. Here, we hypothesized that the HA effect occurs in parallel with the regulation of the plant-associated bacterial community. Rice was grown for 264 h in nutrient solution supplied or not with HA (80 mg L⁻¹). Plant growth was evaluated every 24 h and samples for 16S rRNA gene sequencing were taken after 240 h. The plant's net assimilation rate and the absolute and relative growth rates increased from 100 h to 264 h after the first HA application. The root volume and other growth variables were stimulated at different times along the plant growth cycle. Metataxonomics revealed that bacterial community structure and composition were affected upon HA application. The interactions between members of the community increased in HA-treated roots, showing more connected bacterial communities. Chitinophaga and Mucilaginibacter were the predominant genera in HA-treated roots. These bacteria are reported to produce enzymes that degrade compounds present in the wall of fungi, oomycetes, and nematode eggs. Pseudomonas and Acidobacteria Gp 1, both siderophore-producers and plant-growth promoters were also enriched, although with lower abundances. Given these results, we suggest that plants recruited these microorganisms in response to the stress caused by the HA-root interaction. For the first time, our findings indicate that HA-stimulated plants may adopt the ecological strategy of recruiting members of the bacterial community that are candidates for the suppression of pathogens and, therefore, involved in plant defense.

腐殖酸 (HA) 通过调节激素和氧化还原代谢来刺激几种植物的生长。然而，关于它们与植物相关微生物群的关系的研究几乎不存在。在这里，我们假设 HA 效应与植物相关细菌群落的调节同时发生。水稻在提供或不提供 HA（80 mg L ^-1）。每 24 小时评估一次植物生长情况，并在 240 小时后采集样本进行 16S rRNA 基因测序。第一次施用透明质酸后，植物的净同化率以及绝对和相对增长率从 100 小时增加到 264 小时。根体积和其他生长变量在植物生长周期的不同时间受到刺激。Metataxonomics 显示细菌群落结构和组成受到 HA 应用的影响。在 HA 处理的根中，群落成员之间的相互作用增加，显示出更多连接的细菌群落。Chitinophaga和Mucilaginibacter是在HA-处理的根部的主要属。据报道，这些细菌会产生酶来降解存在于真菌、卵菌壁中的化合物，和线虫虫卵。假单胞菌和酸杆菌 Gp 1，铁载体生产者和植物生长促进剂也被富集，尽管丰度较低。鉴于这些结果，我们建议植物吸收这些微生物以应对由 HA 根相互作用引起的压力。我们的研究结果首次表明，HA 刺激的植物可能采用招募细菌群落成员的生态策略，这些成员是抑制病原体的候选者，因此参与植物防御。