Enriched and depleted microbes at phyla level in humic acid (HA) fertilizer associated with delayed drought responses in maize

Background: Humic acid (HA) fertilizer was previously considered to be able to enlarge the effective absorption area of roots and promote plant root growth. While recent evidences suggested that certain root-associated microbes might be able to mitigate the negative responses of drought stress. In this study, we sought to explore abundance and diversity of root-associated bacterial communities under humic acid (HA) fertilizer and drought stress treatments. Results: We collected rhizospheres of three groups (HA, drought, and control) and microbiomes from bulk soil during flowering period in maize. We obtained the bacterial community for the V4 region of the 16S rRNA gene using Illumina Hiseq2500. By analyzing the sequencing data, we identified 40 bacteria phyla across samples. The abundance level of the 12 bacterial communities at phyla level are significantly different in the rhizosphere of the drought treated samples as compared to the controls, two of which, Actinobacteria and Bacteroidetes, were also significantly enriched (FC=1.79, adj.P=0.043) and depleted (FC=0.70, adj.P=0.086) in HA fertilizer treated samples. Conclusions: The results suggested that the delayed responses of plants to drought stress in HA fertilizer treated soils might be through supply a resource of substance to recruit drought-resistance microbiomes.