4.1 | Differences in microbial richness and composition
between rhizosphere and non-rhizosphere
Our results demonstrated that the
microbial
communities differed markedly between rhizosphere and non-rhizosphere in
richness and composition in this grassland ecosystem. The rhizosphere
microbial richness was lower than that in non-rhizosphere (Figure 1),
which
is in line with previous findings that the microbial diversity decreased
with decreasing distance to plant roots (Donn et al., 2015; Fan et al.,
2017). Such a difference can be explained by a mechanism that
rhizosphere microbiomes are derived from non-rhizosphere microbiomes
under selection effect of host plants (Hartmann et al., 2009; Nan et
al., 2020).
The microbial composition also differed greatly between the two regions
(Figure 1c,d). This was especially evident for the relative abundances
of dominant microbial taxa. The relative abundance ofProteobacteria , a dominant bacterial phylum, was 23.6% in
non-rhizosphere, but increased to 74.4 % in rhizosphere (Figure 1e;
Table S2), likely due to its strategy in nutrient use.Proteobacteria is a representative copiotrophic bacteria phylum
(Nie et al., 2018; Zhang et al., 2018; Zhang et al., 2020). Increased
availability of nutrient in rhizosphere due to the acid activation by
root exudates (Cesco et al., 2010) fosters its growth, because more
nutrients facilitate the copiotrophic bacteria but restrain the
oligotrophic bacteria according to the oligotroph-copiotroph hypothesis
(Fierer, Bradford, & Jackson, 2007; Leff et al., 2015). Similarly,Ascomycota is a dominant fungal phylum, and its relative
abundance increased from 38.6% in non-rhizosphere to 48.8% in
rhizosphere (Figure 1f; Table S2). Such a difference in relative
abundance of Ascomycota between two regions has also been
observed in an alpine grassland (Jiang et al., 2021). Collectively,
these results suggest that the plant rhizosphere microenvironment may
facilitate the flourishing of certain bacterial and fungal taxa.