The trait observations included in FRED have been collected from many different types of roots. You may want to consider selecting only a subset of these roots for your analysis (for example, living, absorptive fine roots only).
In addition to important root traits such as diameter (or diameter class) and color, ancillary root sampling metadata can facilitate accurate comparisons of root traits within- and among species by indicating whether roots were:
1. Fine roots, coarse roots, belowground stems, rhizomes, a mixture of these organs, or the total root or belowground system
2. A given age
3. Associated with a specific root functional class (e.g., absorptive or transport fine roots, or a mixture of both) or heterorhizy class (e.g., fibrous or pioneer roots)
4. Associated with a specific root order (generally 1-7)
5. Ordered according to a centripetal or centrifugal numbering scheme
6. Living or dead (or a mixture of both)
7. Collected from a given soil depth.
In turn, ancillary data associated with plant growing conditions indicate the conditions under which the root traits were measured, for example, whether roots were:
1. Collected outdoors from plants growing in situ or in pots or collected indoors from pots, chambers, or hydroponic solutions
2. Collected from across observational gradients, or from experimental treatments that included nutrient, water, temperature, elevated [CO2], burning, disturbance, girdling, or light manipulations and their associated controls
These are only a few of the many ways in which the root trait observations in FRED can be organized for comparison.