Deciphering the response of nodule bacteriome homeostasis in the bulk soil-rhizosphere-root-nodule ecosystem to soil...

Microplastic polyethylene (PE) is one of the most widely distributed pollutants in agricultural soils. However, its effects on the assembly and co-occurrence of the coevolved bacteriome of legume plants, especially on nodule bacteriome homeostasis, remain unclear. We analyzed nodule numbers, the difference between leaf δ¹⁵N and soil δ¹⁵N (Δδ¹⁵N), and bacterial communities from nodule, root, rhizosphere, and bulk soil under different microplastic PE treatments. We found that microplastic PE treatments accelerated nodulation, resulting Δδ¹⁵N decreased from -2.48 ‰ to -5.06 ‰. The microplastic PE treatments promoted the enrichment of nodule species from the root at an early stage with a source ratio increasing from 0.4 % to 46.6-89.6 %, and reduced selection on the nodule bacteriome with an increase in drift (from 2.8 % to 14.3-36.0 %), probably benefiting the function of Bradyrhizobium in the microbial network whose edges or molecularity increased. In the root, microplastic PE treatments resulted in an increase in homogeneous selection (increase from 29.2 % to 42.8-77.8 %) on the root bacteriome. This study provides new evidence that microplastics can promote nodulation and biological N fixation, revealing a mechanism by which microplastics change nodule bacteriome homeostasis in an Afisol.