Figure legends
Figure 1 Schematic diagram showing vertical root-placement
patterns of individual species within the 0-30 cm soil zone. Each number
in the box indicates a unique species with the solid black lines
indicating species-specific roots. For each soil cube, species
root-placement patterns were assigned with one of the seven possible
rooting types based on their root depths. In the scenario of vertical
root aggregation, species with similar root-placement patterns (a) or
relative root distributions (b) are more likely to co-occur. In the
scenario of vertical root segregation, species with different
root-placement patterns (c) or relative root distributions (d) are more
likely to co-occur. The width of the shapes in panel (b) and (d) is
proportional to the species’ relative root abundance.
Figure 2 Root species richness (a) and relative root abundance
(b) along the 0-100 cm soil profile. Different letters indicate
significant difference among soil zones.
Figure 3 Relative root distributions for the 53 most common
species within the 0-30 cm soil zone. Panel (a) shows the frequencies of
species occurrences in the 0-10, 10-20 and 20-30 cm soil zones. Panel
(b) shows the frequency distribution of species relative root abundance
in the 0-10 cm soil zone. Species with asters suggest that soil zone had
a significant effect on their relative root distributions, based on
which the 53 species were grouped into five groups. Group A, relative
root abundance in the 0-10 cm soil zone was significantly higher than
the deeper two zones, while the deeper two showed no significant
difference; Group B, relative root abundance in the 0-10 cm zone was the
highest and it decreased significantly toward the deeper zones; Group C,
relative root abundance did not differ significantly among soil zones;
Group D, relative root abundance was the highest in the 0-10 cm soil
zone while for some species, relative root abundance in the 20-30 cm
zone was higher than the 10-20 cm zone; Group E, relative root abundance
was the highest in the 10-20 soil zone; ns, nonsignificant. *P< 0.1, **P < 0.05, ***P <
0.01.
Figure 4 Vertical root segregation evaluated based on
root-placement patterns (a) within the 0-30 cm soil zone and relative
root distributions (b-d) in the 0-10 cm soil zone. The similarity in
relative root abundance of co-occurring species was evaluated with mean
pairwise functional distances (MPD; b), standard deviation (SD; c) and
variance (Variance; d). The histograms illustrate the frequency
distribution of the standardized effect size of the corresponding
parameters across 604 root neighbourhoods. In panel (a), a positive
value indicates that co-occurring species in the 0-30 cm soil zone
tended to avoid co-occurring in the same soil zone, whereas a negative
value indicates that co-occurring species were more likely to co-occur
in the same soil zone than expected. In panels (b)-(d), a positive value
indicates that co-occurring species tended to avoid placing similar
relative root abundance in the 0-10 cm soil zone, whereas a negative
value indicates that co-occurring species tended to place more similar
relative root abundance than expected in the 0-10 cm soil zone. The
dashed red line in each panel indicates the mean value of the
standardized effect size of the corresponding parameters.
Figure 5 Pairwise correlations of relative root abundance for
the 29 most common species in the 0-10 (a), 10-20 (b) and 20-30 cm (c)
soil zone. Black solid lines link two species with significant positive
correlations, whereas blue dashed lines link two species with
significant negative correlations. The size of the lines is proportional
to the strength of the correlations.