Shift of allelochemicals from Sorghum halepense in the soil and their effects on the soil's bacterial community: Shift of phytotoxins from S. halepense in soil

Johnsongrass (Sorghum halepense [L.] Pers.), an exotic invasive weed in China, secretes the phenolic compounds, p-hydroxybenzoic acid (p-HBA) and p-hydroxybenzaldehyde (p-HBAL), as the dominant allelochemicals in the root exudates. To better understand how these two allelochemicals affect the soil microbial community in the rhizosphere of S. halepense, the fate of these compounds in the invaded soil and the effect of these phytotoxins on the soil bacterial community were evaluated. The concentrations of the allelochemicals in the soil were determined by a high-performance liquid chromatography-ultraviolet/photodiode array after 1, 2, 4, 6, 12 and 24 h of treatment. MiSeq sequencing was undertaken to understand how the bacterial populations in the soil were affected by the allelochemicals. The HPLC results indicated that p-HBA was degraded by the microorganisms that were present in the soil after 1 h and disappeared after 6 h of incubation. The compound, p-HBAL, initially was converted to p-HBA and then the p-HBA broke down, disappearing after 12 h of incubation in non-sterile soil. Both p-HBA and p-HBAL were stable under sterile soil conditions for up to 24 h. The relative abundance of Proteobacteria was significantly inhibited. However, those of Acidobacteria, Chloroflexi, Verrucomicrobia and Cyanobacteria were increased by the p-HBAL treatment. These findings suggest that allelochemicals from S. halepense might affect the bacterial community composition in the soil.