Table 2.
Traits at different observation scales for a comprehensive, hierarchically ordered core data set to classify root systems, common measurement methods, and Scopus database hits from keyword search.
| Hierarchical level | Parameter | Method | Hits |
|---|---|---|---|
| Whole plant traits | Root biomass | Dry weight | 2166 |
| Root: shoot ratio | 1165 | ||
| Root system shape | Maximum rooting depth | Excavation | 27 |
| Maximum lateral extension | Curve fitting to morphological data | 1 | |
| Depth distribution | 303 | ||
| Lateral distribution | 41 | ||
| Root developmental traits | Number of seminalroots | Root observation on young plants (e.g., gel chambers, blotting paper) | 53 |
| Emergence of shoot-borne roots | 18 | ||
| Initiation of lateral branching | 13 | ||
| Maximum number of lateral branching orders | 8 | ||
| Root branching traits | Average branching angle | 2D and 3D in situ observation and image analysis | 10 |
| Distance between lateral branches | 2 | ||
| Link length (internal, external) | 4 | ||
| Topology (magnitude, external path length, altitude) | 23 | ||
| Axes morphology | Root length (surface) density | Destructive sampling (soil cores) and image analysis | 473 |
| Average root diameter | 550 | ||
| Root length/surface per diameter class | 90 | ||
| Decrease of root diameter per root order | 13 | ||
| Specific root length | 249 | ||
| Root anatomical and physiological traits | Xylem vessel number and diameter | Root anatomical cuts and microscopic measurement | 153 |
| Cortex thickness | 51 | ||
| Suberization/lignification | CO2-flux | 36 | |
| Root respiration | 422 | ||
| Aquaporin abundance | PCR | 308 |