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Root diameter and rooting depth lead to morphological and architectural heterogeneity of plant roots; however, little is known about their effects on root-associated microbial communities. Bacterial community assembly was explored across 156 samples from three rhizocompartments (the rhizosphere, rhizoplane, and endosphere) for different diameters (0.0–0.5 mm, 0.5–1.0 mm, 1.0–2.0 mm, and>2.0 mm) and depths (0–5 cm, 5–10 cm, 10–15 cm, and 15–20 cm) of soybean [Glycine max (L.) Merrill] root systems. The microbial communities of all samples were analyzed using amplicon sequencing of bacterial 16S rRNA genes. The results showed that root diameter significantly affected the rhizosphere and endosphere bacterial communities, while rooting depth significantly influenced the rhizosphere and rhizoplane bacterial communities. The bacterial alpha diversity decreased with increasing root diameter in all three rhizocompartments, and the diversity increased with increasing rooting depth only in the rhizoplane. Clearly, the hierarchical enrichment process of the bacterial community showed a change from the rhizosphere to the rhizoplane to the endosphere, and the bacterial enrichment was higher in thinner or deeper roots (except for the roots at a depth of 15–20 cm). Network analysis indicated that thinner or deeper roots led to higher bacterial network complexity. The core and keystone taxa associated with the specific root diameter class and rooting depth class harbored specific adaptation or selection strategies. Root diameter and rooting depth together affected the root-associated bacterial assembly and network complexity in the root system. Linking root traits to microbiota may enhance our understanding of plant root-microbe interactions and their role in developing environmentally resilient root ecosystems.

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Soil microbial communities are crucial for regulating the stability and degradation of contaminated land. However, the temporal response strategies of particular microbial groups to biotic introductions and their contributions to ecosystem functions and services (i.e., ‘multifunctionality’) in contaminated soils have yet to be investigated. Here, we present results from a 90‐day microcosm experiment aiming to evaluate the temporal changes in bacterial communities and functions in response to microbial and plant additions in a contaminated agricultural soil. In addition, we quantified the contributions of specific bacterial taxa with different response strategies over time to alterations in ecosystem multifunctionality in pollutant degradation (polyphenol oxidase) and the cycling of carbon (dehydrogenase), nitrogen (urease and available nitrogen), phosphorus (available phosphorus), and potassium (available potassium). Results showed that native bacterial communities exhibited strong resilience to the introduced microbial consortium and were altered by plant growth. Plant‐enriched bacterial taxa were located in the core and central positions of the co‐occurrence networks and had considerable influence on the other nodes. Plant growth substantially influenced soil multifunctionality, in a process driven by specific bacterial taxa with different response strategies. The more tolerant taxa contributed most to multienzyme activities, whereas the more affected taxa largely determined multinutrient levels in the soil. These results provide a new perspective in disentangling the roles of plant‐associated bacteria in the assembly of community interactions and ecosystem multifunctionality of contaminated agricultural soils.

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