2.6 Inferring local community assembly mechanisms
To quantify the relative importance of ecological processes in structuring the bacterial and fungal metacommunity, the iCAMP approach was employed(Ning et al., 2020), which is a more sophisticated development of the approach proposed by Stegen et al. (Stegen et al., 2013; Stegen, Lin, Konopka, & Fredrickson, 2012). The iCAMP approach uses a quantitative framework to infer community assembly mechanisms through a phylogenetic-bin-based null model analysis. Within this framework, ecological processes are divided into five processed, including homogeneous selections (HoS), heterogeneous selections (HeS), dispersal limitation (DL), homogenizing dispersal (HD) and drift (DR) processes. In the approach, multiple phylogenetic bins were generated based on the phylogenetic tree. The null model analysis within each bin is calculated by beta Net Relatedness Index (βNRI) and modified Raup–Crick metric (RC). The fraction of pairwise comparisons with βNRI < − 1.96 is considered as the percentages of homogeneous selection, whereas those with βNRI > +1.96 as the percentages of heterogeneous selection. Next, taxonomic diversity metric RC is used to partition the remaining pairwise comparison with |βNRI| ≤ 1.96. The fraction of pairwise comparisons with RC < − 0.95 is treated as the percentages of homogenizing dispersal, while those with RC > + 0.95 as dispersal limitation. The remaining ones with |βNRI| ≤ 2 and | RC | ≤ 0.95 represent the percentages of drift. The βNRI and RC are calculated using the “picante” package(Kembel et al., 2010) and “iCAMP”(Ning et al., 2020) package in R.