Environmental gradients retain the key dimensions of the root economics space at the community level

The root economics space (RES) provides a framework for understanding species-level belowground strategies, but niche differentiation and environmental filtering may cause community-level root trait coordination to diverge from species-level patterns. Here, we compiled fine-root trait data measured directly from bulk soil samples across 302 plant communities worldwide to examine community-level root trait coordination and its climatic and edaphic drivers. Analyses based on a subset of communities with complete RES traits revealed two major dimensions of variation that were partly consistent with, but not identical to, the classical species-level RES framework. A collaboration-related axis, mainly defined by root diameter and specific root length, was associated with soil pH, with near-neutral soils linked to trait combinations consistent with more "do-it-yourself" nutrient acquisition and acidic soils associated with patterns suggesting greater reliance on mycorrhizal "outsourcing" pathways. A second fast-slow axis, characterized by root tissue density, root nitrogen concentration and root diameter, was associated with precipitation and temperature gradients, with drier environments linked to more conservative trait syndromes and humid, cooler environments associated with more acquisitive strategies. Root nutrient traits also showed ecosystem-specific patterns: in forests, root nitrogen tended to decrease whereas root phosphorus increased along soil nutrient gradients, while in grasslands, root nitrogen increased with soil total nitrogen. Overall, community-level fine-root traits retained key structural elements of the RES framework while exhibiting context-dependent deviations from species-level expectations. These findings highlight how environmental gradients shape belowground trait organization across communities and improve our understanding of plant nutrient-acquisition strategies at large spatial scales.