Flooding episodes and seed treatment influence the microbiome diversity and function in the soybean root and rhizosphere.

Climate change-related events such as flooding have threatened crop productivity, agricultural sustainability, and global food security by causing hypoxic conditions. Such conditions impaire root development and nutrient acquisition, and alter root rhizospheric microbial communities that are vital for plant health and productivity. Seed treatment with pathogen protection have been key to maintaining early seed germination and plant productivity in field conditions. Still, their role in flooding stress and microbiome diversity and functionality in soybeans is poorly understood. Here, we performed field-based investigations to understand the impact of flooding episodes (0, 3, and 7 days after floodings; DAF) and seed treatment (Cruiser MAXX) on soybean plant growth and rhizosphere microbiome diversity and functionality. Flooding episodes significantly reduced seed yield (746 kg ha) compared to untreated control. However, the seed treatment increased plant height and pods per plant (3-DAF) and reduced flood injury by 33 % (7-DAF). The shotgun metagenomic analysis showed that seed treatment significantly enhanced the microbial community in rhizospheric soil. Flooding episodes impacted the microbial communities with higher abundance at 3-DAF than at 7-DAF. Flooding stress reduced the microbial diversity, although Proteobacteria increased as root endophytes. Seed treatment and flooding combinations decreased microbiome functionality and reduced gene counts for phytohormone biosynthesis, fermentation, nitrogen, symbiosis, and degradation pathways. Similarly, flooding stress shifted the carbohydrate synthesis to a more specialized substrate. These findings enhance understanding of soybean root and rhizosphere microbiome diversity and functionality dynamics during flooding stress and provide a platform to develop sustainable agricultural practices for enhancing soybean stress tolerance to flooding.