Microplastics Boost Soil Multifunctionality via Enhancing Competitive Co‐Occurrence of Bacterial Communities in Drylands

ABSTRACT The interactions among bacterial communities can affect service functions of soil ecosystems. It is unclear how the change in soil ecosystem multifunctionality (SEMf) shifts with the adaptive modification of interactive relationships among bacterial communities in response to microplastic (MPs) stress. To address this gap, we conducted field observations by introducing the MPs with different morphologies (spheres, fibers, fragments, and powders) and concentrations (0.01%, 0.1%, and 1%) into topsoil for 2 years to investigate the long‐term effects of MPs on SEMf and its mechanisms. Generally, MPs addition significantly promoted the supporting capacity of bacterial community diversity for SEMf ( R 2 = 0.169, p = 0.000). Ordinary least‐squares regression and general linear models confirmed that the changes in SEMf were closely associated with the co‐occurrence relationships among bacterial communities ( R 2 = 0.573), particularly network nodes and modularity ( R 2 = 0.766). MPs significantly promoted the SEMf by 9.6% ( p = 0.023) and altered the bacterial competition‐cooperation ratio ( p < 0.05). Competitive relationships were positively associated with the SEMf (pearson's r = 0.757), whereas cooperative relationships affected it negatively (pearson's r = −0.757). Overall, the competition relationships exhibited stronger explanatory power for the changes in SEMf than cooperative ones ( R 2 = 0.766 vs. 0.735). This study proposes a microbial competition‐SEMf promotion hypothesis (competition‐promotion hypothesis), which provides a key insight into the shift of SEMf when exposed to MPs stress. MPs strategically drove the transition from cooperation‐ to competition‐dominated relationships among bacterial communities, thus generating overall positive effects on SEMf in drylands.