Mean root diameter, specific root length (SRL), root length
and diameter class distribution were heavily influenced by soil
bulk density but the soil type did not have any significant effect
(Table 2). Mean root diameter was positively correlated with soil
bulk density (Table 2) and SRL negatively correlated with soil bulk
density (Fig. 1a), showing a 64% reduction with a 25% bulk density
increment. The length of different root orders was strongly
affected by soil compaction. Thus, an increase in soil compaction
decreases the proportion of fine roots (diameter between 0 and
0.5 mm) whereas the proportion of medium and high diameter
roots (between 0.5 and 1.5 mm) was increased with soil compaction
(Fig. 1b). These changes in root size class distribution with soil
compaction were visually evident (Fig. 2), where a reduction of second
and third root order can be seen at the same time as the first
root order was incremented with soil compaction. Despite these
changes in the general root morphology pattern, root tissue mass
density (TMDR) was not affected by soil compaction or soil type