FIGURE 2 Differential abundance of bacterial (A) and fungal (B) OTUs in the rhizosphere soil of different samples (at the phylum level). The Welch T-test was used for statistical analysis. The Bonferroni method was used for multiple hypothesis test correction. ‘*’: P<0.05, ‘***’: P<0.01.
3.5 | Core microbial community
As shown in Figure 3, 5,017 bacterial OTUs were detected in the three families. Among them, 1,221 OTUs were found in all samples, accounting for 24.34% of all OTUs. OTUs with an abundance of more than 1% were selected as representative of the core bacterial family. These OTUs were assigned to various genera. Within Acidobacteria,norank_Subgroup2 accounted for the largest proportion of the genera (containing 12 OTUs, with a relative abundance of 75.32%), followed by norank_Acidobacteriales (3 OTUs, relative abundance 14.00%). Acidibacter (4 OTUs, relative abundance 34.19%),norank_Xanthobacteraceae (2 OTUs, relative abundance 19.85%),Burkholderia-Caballeronia-Paraburkholderia (2 OTUs, relative abundance 19.14%), and Bradyrhizobium (1 OTU, relative abundance 8.91%) were the most abundant in Proteobacteria, and HSB_OF53-F07 was the most abundant in Chloroflexi (1 OTU, relative abundance 2.90%). In the box plots corresponding to each bacterial genus, the abundances ofAcidothermus and Bryobacter in Acidobacteria showed a trend of leveling off or decreasing first and then increasing, respectively, with increasing carbon sequestration. However, the relative abundance of each genus in Proteobacteria and Chloroflexi decreased to different degrees with the increase in carbon sequestration in the samples (Figure 3).
A total of 2,300 fungal OTUs were detected in the three families. Among them, 254 OTUs were found in all samples, accounting for 11.04% of all fungal OTUs. According to the bacterial classification method, these OTUs belonged to unclassified_Basidiomycota (1 OTU, relative abundance 33.74%), Russula (1 OTU, relative abundance 26.36%),Saitozyma (1 OTU, relative abundance 19.30%) andGeminibasidium (1 OTU, relative abundance 19.16%) in Basidiomycota. Unclassified_Ascomycota (4 OTUs, relative abundance 37.91%), Penicillium (1 OTU, relative abundance 32.25%), Archaeorhizomyces (2 OTUs, relative abundance 14.32%),Oidiodendron (1 OTU, relative abundance 6.70%), andunclassified_Helotiales (1 OTU, relative abundance 4.89%) were the most abundant genera in Ascomycota, and Umbelopsis (1 out, relative abundance 4.38%) was the most abundant in Mucoromycota. In the box plots, in Basidiomycota, the relative abundance of all genera exceptSaitozyma showed an increasing trend with the increase in carbon sequestration. However, the relative abundances of fungi in Ascomycota and Mucoromycota showed a continuously decreasing trend except that the relative content of Penicillium decreased first and then increased (Figure S2).