FIGURE 3 Bacterial communities in the core rhizosphere of different samples. The inner (various colors) and outer (yellow) pie charts represent the core bacterial phyla and genera, respectively. The size of each phylum and genus in the pie chart represents their contribution to the overall abundance. The box plots show the relative abundance of the corresponding genus in the different samples. Some genera appeared in the taxonomy database with no corresponding scientific name and are labeled ‘norank’.
3.6 | Relationships between the rhizosphere microbial community and soil environmental factors
The RDA results show that for bacteria, the first axis explained 53.97% of the variation in the data, and the second axis explained 14.06%, representing a cumulative explanatory power of 68.03% (Figure 4A). The first two axes reflected the relationships between the genera and their influencing factors well. As shown in Figure 4A, norank_Subgroup 2 had the strongest correlation with environmental factors, whilenorank_Gemmataceae had the weakest correlation. On the other hand, Acidothermus was greatly affected by the total organic carbon, total nitrogen content and C/N but was less affected by pH and soil moisture. Norank_Xanthobacteraceae andnorank_Acidobacteriales had strong positive correlations with pH and soil moisture and weak correlations with altitude, total organic carbon, total nitrogen and C/N. For the fungi, Figure 4B shows that the first axis explained 35.27% of the variation, and the second axis explained 27.06%, representing a cumulative explanatory power of 62.87%. Of the top 10 fungal genera, unclassified_Basidiomycota andunclassified_Fungi showed strong positive correlations with total organic carbon, total nitrogen, moisture, C/N and pH, as didSebacina .
The heatmap results show that, for the bacteria, there was a very significant positive correlation between norank_Subgroup2 and soil moisture (P<0.01). There was a significant negative correlation between norank_Elsterales and pH (Figure 4C). OfAcidibacter , Acidothermus and Bryobacter , the three confirmed genera, Bryobacter had a significant negative correlation with pH and moisture (P<0.05), andAcidothermus showed a significant positive correlation with total organic carbon and total nitrogen. For the fungi, there was a significant positive correlation between Sebacina and total organic carbon and total nitrogen (P<0.05). There was a significant negative correlation between Saitozyma and soil pH (Figure 4D). The other microorganisms showed different degrees of positive and negative correlation with environmental factors, but none of these correlations were significant. The analysis results shown in the heatmap are consistent with the RDA.