3.2 Rare taxa were mainly responsible for microbial
spatial scaling patterns
We first investigated whether abundant and rare subcommunities followed
similar spatial scaling patterns, such as TAR and DDR (Fig. 2a and b).
The typical community richness and Bray-Curtis similarity were
respectively used to quantify TAR and DDR. As a result, clear TAR
(z = 0.494, P < 0.001) and DDR (d =
-0.242, P < 0.001) patterns were observed for the
bacterial communities (Fig. 2a and b). As expected, stronger TAR pattern
was found for rare subcommunities (z = 0.517, P< 0.001) than abundant subcommunities (z = 0.029,P = 0.034) (Fig. 2a). Similarly, rare subcommunities (d =
-0.447, P < 0.001) harbored stronger DDR patterns than
abundant subcommunities (d = -0.12, P < 0.001)
(Fig. 2b). For both TAR and DDR, rare subcommunities even showed
stronger spatial scaling patterns than the whole community. The results
suggested that rare subcommunities were mainly responsible for the
spatial scaling patterns followed by microbial communities.
To verify the major contribution of rare subcommunities to the spatial
scaling patterns of microbial communities, we extended both alpha- and
beta-diversity to Hill numbers to analyze TAR and DDR patterns at
different diversity orders. As such, the ambiguous definition of
abundant and rare taxa can be well resolved by giving continuously
decreasing weight on rare taxa. By setting the diversity order qto different values (here 0 ≤ q ≤ 2), different weight is given
to microbial taxa with different relative abundance. The higher
diversity order q is, the lower weight is given to rare taxa.
Taking alpha diversity for example, the Hill numbers equal to community
richness when q = 0, indicating all microbial taxa are equally
treated. When the order q is set to 1 and 2, the Hill numbers
respectively equals to the Shannon-Wiener and Simpson diversity index
(Supplementary Figure 4). In the case rare subcommunities were mainly
responsible for the microbial spatial scaling patterns, decreased
DARq and DDRq slope coefficients with
increasing q values were expected. As a result, sharply decreased
slope coefficients of DARq and DDRq were
observed when the diversity order q increased from 0 to 2 (Fig.
2c). Such results confirmed that rare subcommunities were mainly
responsible for the observed spatial scaling patterns followed by
microbial communities.