# Table 1 Traits description

Trait Units Description
Bushiness (Bush) n/n The ratio of the maximum to the median number of roots
Convex area (ConvA) c m 2 The area of the convex hull that encompasses the root.
Network depth (Ndepth) cm The number of pixels in the vertical direction from the upper-most network pixel to the lower-most network pixel.
Network Length Distribution (Ldist) n/n The fraction of network pixels found in the lower 2/3 of the network. The lower 2/3 of the network is defined based on the network depth.
Major axis (MajA) cm The length of the major axis of the best fitting ellipse to the network
Network Width (Nwidth) cm The number of pixels in the horizontal direction from the left-most network pixel to the right-most network pixel. Only pixels lying in the same row are considered.
Maximum number of roots (MaxR) n After sorting the number of roots crossing a horizontal line from smallest to largest, the maximum number is considered to be the 84th-percentile value (one standard deviation).
Average root width (Width) cm The mean value of the root width estimation computed for all pixels of the medial axis of the entire root system. This trait corresponds to diameter of a root.
Median number of roots (MedR) n The result of a vertical line sweep in which the number of roots that crossed a horizontal line was estimated, and then the median of all values for the extent of the network was calculated.
Minor axis (MinA) cm The length of the minor axis of the best fitting ellipse to the network
Network area (NwA) c m 2 The number of network pixels in the image.
Perimeter (Perim) cm The total number of network pixels connected to a background pixel (using a 8-nearest neighbor neighborhood).
Aspect ratio (AspR) cm/cm The ratio of the minor to the major axis of best fitting ellipse
Network solidity c m2/c m2 The total network area divided by the network convex area.
Specific root length (SRL) cm/c m3 Total network length divided by network volume. Volume is estimated as the sum of cross sectional areas for all pixels of the medial axis of the root system. The total root length is the number of pixels in the medial axis of the root system.
Network Surface Area (Nsurf) c m 2 The sum of the local surface area at each pixel of the network skeleton, as approximated by a tubular shape whose radius is estimated from the image.
Network length (Nlen) cm The total number of pixels in the network skeleton.
Network volume (Nvol) c m 3 The sum of the local volume at each pixel of the network skeleton, as approximated by a tubular shape whose radius is estimated from the image.
Network width to depth ratio cm/cm The value of network width divided by the value of network depth. 