Toward refining and contextualizing the root economics space

The trait-based 'root economics space' (RES) offers a framework for understanding plant belowground strategies. It is structured along two axes: a 'fast-slow' conservation gradient and a 'do-it-yourself to outsourcing' collaboration gradient. However, growing evidence reveals divergent dominant trait combinations structuring the RES axes across plant types and environmental contexts, challenging the framework's generality. We propose an RES framework that refines and contextualizes these axes by incorporating functionally relevant root traits. It explicitly accounts for differences in symbiotic strategies among arbuscular, ectomycorrhizal, and ericoid associations, while also considering dual-mycorrhizal and nonmycorrhizal types, and integrating nutrient limitation patterns across ecosystems. We further define the spatial scales and organizational levels at which the RES framework is most applicable to guide its future development.