Summary From a root economics perspective, variation in fine‐root morphological traits reflects contrasting strategies of resource acquisition and conservation. Here, we examined how fine‐root structural and functional traits are associated with belowground architecture. We analysed coarse‐root architecture and fine‐root functional traits (specific root length, dry matter content and diameter) in four tap‐rooted and four adventitious‐rooted perennial herb species from North Patagonian forests. We considered two scales of analysis: entire belowground systems and root modules. Variations in the dry‐matter content and specific length of fine roots were stronger among species than between architectural groups. Only for tap‐rooted plants, lower specific root length was related to the development of thicker and more branched second‐order roots. Dry‐matter content of fine roots was positively related to the belowground mass fraction in tap‐rooted plants and negatively related to adventitious‐rooted plants. At root‐module scale, the diameter of fine roots was more variable and more related to the structure of exploratory roots in tap‐rooted species. Our multiscale approach strongly suggests that belowground architecture of coarse‐root systems constrains fine‐root functional strategies. Tap‐rooted species exhibited a more integrated and architecturally constrained belowground system than adventitious‐rooted species.