Rhizosphere bacteriome assemblage following initial fluctuations is delayed with nitrogen additions in tomato seedlings

Little is known about how seedlings sense new soil environments and how the rhizosphere bacteriome changes accordingly. It is important to elucidate these changes to better understand feedbacks that contribute to nutrient cycling and plant fitness. Here, we explored how the tomato rhizosphere bacteriome developed weekly throughout the vegetative developmental stage and with variable nitrogen (N) fertilizer additions. Bacterial communities expressing diverse functions highly fluctuated in the first and second week after planting, and these fluctuations diminished progressively after the third week. Bacteria capable of biocontrol stabilized after the fourth week, while those involved in nutrient cycling continued to change in abundance week-to-week. Thus, bacterial specialization may be concomitant with bacteriome stabilization. With N fertilizer application, bacteria with diverse functions continued to fluctuate through the fifth week. However, regardless of fertilization, bacterial communities stabilized by the sixth week. It may take two weeks for roots to select for soil bacteria to assemble a specific rhizosphere bacteriome, but when N is applied, this period extends. Subsequently, roots may select for bacteria that are already established in the rhizosphere rather than from the bulk soil. This study showcases the dynamics of rhizosphere assemblage and how this process is affected by N additions.