Discussion
Widespread species masked thebiogeographic patterns of microbes
Nearly half of the reported NTF species (N = 44) in 3 genera were found during this study. At the species level, the distribution pattern was random and had no heterogeneous pattern. The number of common species only accounted for less than 5% of the total species but contributed to 70% of the OF. When excluding the 4 widespread species, the pattern tended to be non-random with a clear heterogenous pattern. If the distribution of the species with high OF were gradually superimposed, the patterns of NTF tended to be random. The results indicated that the extreme high OF and wide distribution of the common species mask microbial heterogeneous biogeographic patterns.
The 31 rare species were restricted to 0.44% ~ 9.21% of the sampling sites. The genera Dactylella andDrechslerella were restricted in 7.02% and 7.89% of the sampling sites respectively. Because the limited distribution and the existence of endemic species were representative of the biogeographic pattern in itself5, we concluded that NTF has heterogeneous biogeographic patterns..Although the rare species were low in abundance, they played a key role in understanding microbial biogeographic patterns. A low sampling effort may have limited any observations of these species. In this study, rare species (OF < 1%) accounted for 70.45% of the 2,250 specimens collected in Yunnan Province. Had the sampling effort been reduced by 10%, we estimated that 29 of all species (93.54% of rare species) would have been more difficult to observe. Studies that used metagenomics to investigate microbial diversity patterns reported a sampling intensity interval between 3~300 samples, with an average of 40 samples collected (summarised according to articles published in The ISME Journal and Microbiome over the past five years). Sampling efforts were subsequently reduced to same time and resources when using metagenomic methods (Karimi et al ., 2018). With low sampling efforts, many rare species would be ignored.