Field dynamics of the root endosphere microbiome assembly in paddy rice cultivated under no fertilizer input.

Plants accommodate diverse microbial communities, termed the microbiome, which can change dynamically during plant adaptation to varying environmental conditions. However, the direction of these changes and the underlying mechanisms driving them, particularly in crops adapting to the field conditions, are not well understood. Here, we investigate the root endosphere microbiome of rice (Oryza sativa ssp. japonica) across four consecutive cultivation seasons in a high-yield, non-fertilized, and pesticide-free paddy field, compared with a neighboring fertilized and pesticide-treated field. Using 16S rRNA amplicon and metagenome sequencing, we analyzed three Japonica cultivars-Nipponbare, Hinohikari, and Kinmaze. Our findings reveal that the root endosphere microbiomes diverge based on fertilization regime and plant developmental stages, while the effects of cultivar variation are less significant. Machine learning model and metagenomic analysis of nitrogenase (nif) genes suggest enhanced nitrogen fixation activity in the non-fertilized field-grown roots, highlighting a potential role of diazotrophic, iron-reducing bacteria Telmatospirillum. These results provide valuable insights into the assembly of the rice root microbiome in nutrient-poor soil, which can aid in managing microbial homeostasis for sustainable agriculture.