2.5 Definition of abundant and rare OTUs
In this study, OTUs were classified as abundant or rare in relation to their relative abundances. Briefly, the OTUs with a relative abundance of > 0.1% in all samples were defined as abundant taxa (AT), whereas the OTUs with a relative abundance of < 0.01% in all samples were defined as rare taxa (RT) (Jiao and Lu, 2020; Wan et al., 2021a). Those OTUs with a relative abundance between 0.01% and 0.1% in all samples were defined as intermediate taxa.