Fig. 6: Conceptual framework of differences in bacterial composition by root order.

The composition of root-associated bacteria was most distinct from bulk soil in the lowest root orders, where bacterial abundance was also typically higher. Taxa associated with carbon mineralization were found in greater relative abundance in root orders 1 and 2, suggesting that copiotrophic phyla preferentially colonize absorptive fine roots with greater nutrient flux. R1/2 is colored orange, R3 is green, and R4/5 is blue.