The plant rhizosphere, a region interconnecting roots, soil, and microorganisms, is critical for plant resource acquisition, community structure, and the functional stability of ecosystems. Most studies focus primarily on root traits, while overlooking the covariation within the rhizosphere root–soil–microbe continuum and its ecological implications under environmental change. Here, we highlight the necessity of integrating rhizosphere function into a broader theoretical framework encompassing belowground traits, such as the core functional modules of roots, rhizosphere microorganisms (including mycorrhizal fungi), and soil. We further identify critical knowledge gaps and future directions for research on rhizosphere function traits. This framework expands current perspectives on plant belowground functional traits, plant adaptation, and ecosystem stability under changing environments.