Watersheds are crucial for reveal microbial distribution
patterns
Our results showed that the heterogeneous distribution of microbial
diversity could be better explained by using watersheds as the units
compared with grids. More endemic species were observed using watershed
units (19 species by using watersheds vs 11 species by using grids).
Additionally, 84.21% rare species were clustered in the same or
adjacent watersheds, while only 63.16% were clustered in the same or
adjacent grids.
At the genetic level, the 5 clades of A. oligospora were
consistent with the natural watershed divisions and these divisions were
further supported by machine learning results. The
64.70%,60.71%,80.00%,63.89% and 61.11% of the strains from clade
1 to clade 5 were correspondingly distributed in the Yangtze River, Red
River, Pearl River, Mekong, and Salween-Irrawaddy watersheds
respectively. These findings suggest that watersheds are the most
crucial factor in explaining the observed spatial distribution pattern
of A. oligospora , more so than other environmental factors.
Historical events leading to the formation of Yunnan’s six large
watersheds, including the uplift of Qinghai-Tibet Plateau and the
spatial compression of the Hengduan Mountains, therefore likely shaped
the spatial distribution of NTF genetic diversity. Because environments
in mountainous region were geographically isolated by mountains, rivers,
and other natural barriers, many new species evolved here (Ding et
al ., 2020). As such, patterns of microbial diversity are easier to
observe in this region given its clear watershed boundaries, complex
terrains, high environmental heterogeneity, and abundant biodiversity.
Watersheds with clear boundaries and ecogeographical significance make
them natural division units for biogeographic research. The dividing
ridges between adjacent watersheds are critical dispersal barriers, the
relatively isolated materials and energy flow were shaped. Previous
studies have considered watersheds as ecosystem boundaries, and
discussed the possibility of setting watersheds as the appropriate units
in landscape ecology (Berkes et al., 1998). For example, Paula et
al. (2018) found that watersheds were better units when predicting
diversity based on environmental heterogeneity. The hierarchical
structure of watersheds also makes them appropriate for understanding
how historical and contemporary factors contribute to diversity
patterns. Moving from large scales (secondary or tertiary watersheds) to
smaller scales (sub-watersheds), the influence of ridge barriers
hindering distribution gradually decrease while environmental influences
increase. The effects of historical events and contemporary
environmental background are therefore perfectly coupled by watershed
units. As such, using watersheds research units should help solve most
of the problems in studying the spatial distribution of microbial
diversity.
Meanwhile, from the perspective of watershed, the possibility of
integrating plants, animals and microorganisms biogeographic research
could be provided. As with microorganisms, biogeographic research on
plants and animals is also plagued by confusing or deficient research
units, methods, and analyses. For instance, the biogeographic provinces
between the plants and animals were not coincident. Watershed units can
provide an alternative that is applicable to multiple biological groups,
allowing for research that consider the interactive effects of plants,
animals, and microorganisms in shaping biogeographic patterns. For the
core issues of biogeography, including the historical and environmental
influences on the spatial distribution, the scale effects on the
biological distribution patterns could be also solved. Finally, we
believe that watersheds could support explanations on the origin of
biodiversity, which is a fundamental scientific problem.