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.