Effects of herbicide application on oil palm plantation soil bacterial diversity, function, and co-occurrence networks

Despite the extensive use of chemical controls in weed management programs, the effect of herbicides on soil microbial communities is inconclusive. In this study, the effects of glufosinate-ammonium (T1) and metsulfuron-methyl (T2) application at the recommended rate (495 g a.i./ha and 15 g a.i./ha) on the soil bacterial communities within an oil palm plantation were investigated using 16 S rRNA gene high-throughput sequencing. Herbicides were applied in the rhizosphere area of oil palms, and soil microbial communities were assessed over multiple time-points, for 9 months. Herbicides did not drastically influence the alpha or beta diversity of the soil bacterial community, but a significant decrease in the Shannon and inverse Simpson diversity indices was observed at 6 months after application (MAA) and recovered at 9 MAA in T2. The relative abundance of selected beneficial soil bacteria strains was stable across both herbicide treatments and sampling times. FAPROTAX functional profile prediction showed minimal influence of herbicides on soil bacterial activity and functions. The complexity and stability of the bacterial network had increased in T1 but were reduced in the rhizosphere soil in T2. Herbicide application was shown to increase the abundance of the bacterial phylum Latescibacterota, which may have the potential to metabolise chemical compounds that could be explored for future bioremediation use. Our results suggested that application of glufosinate-ammonium and metsulfuron-methyl at the recommended rate may not adversely affect soil bacterial communities or their functions in oil palm plantations.