3.4 Local community assembly mechanisms also drove the
spatial scaling patterns of microbial communities
To further disentangle the underlying mechanisms driving the spatial
scaling patterns of microbial communities, especially the different
patterns between abundant and rare subcommunities, the following
experimental and statistical investigations were carried out.
First, deep sequencing of a randomly selected sample (BBW11) was
performed to investigate the dispersal potential of microbial
communities. Here, microbial ASVs were mapped to the deep sequencing
dataset at the levels of ASV and read (Fig. 4 a and b). As a result, as
high as 72.62% microbial ASVs and 88.57% reads could be mapped to the
deep sequenced dataset. Dramatically differed mapping ratios were
observed between abundant and rare subcommunities. Abundant ASVs (100%)
and reads (100%) can be completely mapped to the deep sequencing
datasets. In contrast, rare ASVs (65.22%) and reads (74.46%) were
mapped to the deep sequencing datasets at much lower ratios. The results
suggested that abundant taxa had higher dispersal rate and better
adaptability to the environment than rare taxa.
Second, the niche breadth and niche overlap were also calculated using
the Levins’ standardized niche breadth index and the Pianka’s niche
overlap index (Fig. 4c and d). In general, rare ASVs were similar with
the whole community regarding the niche breadth and niche overlap. In
contrast, abundant ASVs had much higher niche breadth and overlaps than
rare ASVs. Such results were consistent with the deep sequencing
experiment and suggested that the abundant taxa can better adapt to the
environment and coexist with each other than rare taxa.
Third, null model analysis was carried out to investigate the links
between local community assembly mechanisms and microbial spatial
scaling patterns. According to βNRI and RCbray values,
the contribution of five different processes to the compositional
variations of microbial communities were quantified, including
homogeneous selection, heterogeneous selection, dispersal limitation,
homogeneous dispersal, and drift (Fig. 5). At the whole community level,
drift (62.32%) is mainly responsible for the compositional variations
of microbial communities, followed by dispersal limitation (24.45%) and
homogeneous selection (10.56%) (Fig. 5a). Distinct community assembly
processes were observed for abundant and rare subcommunities. Abundant
subcommunities were mainly structured by homogeneous selection (38.69%)
and drift (36.55%), whereas rare subcommunities were mainly structured
by drift (58.8%) and dispersal limitation (24.04%) (Fig. 5b and c).
Such differed contributions of homogeneous selection and dispersal
limitation to abundant and rare subcommunities were consistent with the
deep sequencing experiment results. The results here demonstrated that
distinct community assembly mechanisms shaped the compositional
variations of abundant and rare subcommunities, resulting in differed
spatial scaling patterns.