Transcriptomic analysis of humic acid in relieving the inhibitory effect of high nitrogen on soybean Nodulation

Nitrogen fertilizer intake promotes soybean growth before the formation of nodules, but excess nitrogen plays an inhibitory effect on soybean nodulation. It is important to balance nitrogen levels to meet both growth and nodulation needs. In this study, the relieve effect of humic acid on soybean nodulation inhibition under high nitrogen condition was studied, and transcriptomic analysis was used to understand the mechanism. Results showed that lower nitrogen level with 36.4 mg urea per pot can increase the nodule numbers of soybean, and higher nitrogen level with 145.9 mg urea per pot (U4 group) had the best growth indicators, but inhibit nodulation significantly. HA relieved the inhibitory, and the nodule number incresed by 122.1 % compared with U4 group, when 1.29 g HA was added (H2 group). Transcriptome analysis showed a total 2995 differentially expressed genes (DEGs) at the 25th day, accounting for 5.66% of the total annotation gene (44848), under test conditions. These DGEs were enriched in MAPK signaling pathway-plant, flavonoid biosynthesis, plant hormone signal transduction according to -log10 (Pasjust) value in KEGG pathway. Humic acid can be used to blance nitrogen level in soybean planting to control nodule number