Vertical root segregation in root neighbourhoods
Our hypothesis that individual species in root neighbourhoods would be
vertically segregated was generally not supported. Although there were
higher proportions of root neighbourhoods where heterospecific roots
tended to avoid co-occurring (Fig. 4a) or avoid placing similar root
abundance in the same soil zone (Table 1; Fig. 4b-d) than that tended to
co-occur, the proportions of root neighbourhoods that either exhibited
significant root segregation or aggregation were very low and did not
differ substantially (Table 1). Furthermore, the mean of the
standardized effect size of the four parameters measuring rooting
similarity did not differ significantly from zero (Fig. 4), indicating
that the diversity of root-placement patterns in the observed
communities did not differ significantly from that of randomly simulated
distributions. Moreover, in contrast to our prediction, when only roots
that occurred throughout the 0-30 cm soil zone were included in the
analysis, we found a higher proportion of root neighbourhoods that
exhibited root aggregation (54%-76%) than that exhibited root
segregation (24%-47%; Table S4). Such aggregated patterns were
significant in the 20-30 cm soil zone when rooting similarity was
evaluated based on the variance of co-occurring species’ relative root
distribution (Table S4), suggesting that species have similar root
abundance in the 20-30 cm soil zone.