Linking structure and function in tree roots
Plant roots are complex branching structures with multiple branch orders. How these branch orders are separated into groups of roots with distinct structure and function is unclear, limiting our ability to differentiate roots of different functions and to accurately quantify the contribution of different root groups to ecosystem processes. Morphological, anatomical, physiological parameters of each branch order across >100 tree and herb species were examined and key features differentiating roots of different functions were identified.
In woody species, the whole root systems can be separated into two groups, i.e., woody framework roots and non-woody uptake roots. Woody roots are thick, well-protected, long-lived and have high transport capacity but largely lack absorptive capacity whereas non-woody roots are thin, frequently mycorrhizal, intimately associated with rhizosphere biota, short-lived and mainly responsible for resource absorption. The entire root system in herb species may be non-woody but roots can also be separated into a short-lived absorptive root group and a long-lived storage root group. These functional classifications remove the arbitrariness in traditional diameter-class classifications and pave the way for a better understanding of root functions in the plant world.