2.5. Root morphology
A fraction of root biomass of each plant was taken to analyse
the morphological traits. This fraction represented about 20
±
5% of
total root biomass (mean
±
SD), and, in morphological terms, this
fraction represents one of the main roots (first order) linked to the
root-stem connection. This approach prevents the underestimation
of root length caused by the root base, which has a high biomass and
short length. Roots were scanned with a high resolution scanner at
600 dpi in a transparent tray with water. Root analysis was carried
out with image analysis software (WhinRHIZO ver. 2004a, Regent
Instruments Inc., Quebec, Canada). The output of the software gives
the following: mean root diameter, total root length, root volume
and length of each diameter class (between 0 and 4.5 mm). This
software calculates the root volume based on the root diameter
distribution and not only on mean root diameter, so therefore, the
measurements are precise. After scanning, roots were dried at 70 ◦C
to obtain dry biomass. The variables calculated were as follows:
specific root length (SRL) as a ratio of root length and dry mass;
total root length as a product of SRL and dry mass of the whole
root (excluding root base); root tissue mass density (TMDR) was
calculated as a ratio of root dry mass and root volume and root
length ratio (RLR) as a ratio of total root length and plant mass.
Length of each diametric class was expressed as a percentage of
total length considering only the roots’ length of diameter as being
less than 1.5 mm (which represents about 98% of total length for all
cases).