Root architecture and fine-root economic traits in tap- and adventitious-rooted perennial herbs

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.