4.2 Broader environmental adaptations of abundant bacteria
The current study found that abundant taxa were ubiquitous in more than
half of sediment samples, while most rare taxa occurred only in a few
samples (Fig. S1a). These results are in line with previous studies
where abundant taxa with high local abundance have a widespread or
ubiquitous distribution in terrestrial (Ji et al., 2020; Jiao and Lu,
2020; Wan et al., 2021a) and aquatic (Liu et al., 2015; Mo et al., 2018;
Wan et al., 2021b) ecosystems. It is possible that abundant taxa may
grow on a wider array of substrates and occupy a broader niche compared
with rare taxa, hence supporting their persistence at higher abundance
in a wider range of sites (Hambright et al., 2015). Indeed, our
environmental threshold analysis further corroborated this assumption
that abundant taxa exhibited potential broader response thresholds to
the environmental variables compared to rare ones (Fig. 3a). For
example, abundant taxa exhibited broader nutrient utilization potential
than rare taxa, especially for TC, TN, NH4-N, and
NO3-N.
Our results further demonstrated that abundant taxa displayed stronger
phylogenetic signals for environmental preferences compared with rare
taxa (Fig. 3b). This indicates closely related taxa in the abundant
subcommunity exhibit more similar ecological preferences across
environmental gradients than taxa in the rare subcommunity. Several
recent reports have shown that the stronger phylogenetic signals for a
given microbial community of environmental preferences, the greater the
phylogenetic niche conservatism in the evolutionary history of
environmental adaptation (Jiao and Lu, 2020; Wan et al., 2021a). Thus,
the stronger phylogenetic signals of abundant taxa for environmental
preferences may explain why they have broader environmental breadths
than their rare counterparts. In addition, our results revealed that the
correlation between community composition and phylogeny in the rare
subcommunity was stronger than that in the corresponding abundant
subcommunity. This finding implies that abundant taxa are better in
maintaining ecological niches than rare taxa under altered environmental
conditions (Ji et al., 2020). Together, the above findings indicated
that abundant bacterial taxa possessed stronger adaptations to various
environmental conditions than rare bacteria in sediments of the Yarlung
Tsangpo River.