Effects of inoculation on soil microbial communities
A total of 506 fungal ASVs and 4808 bacterial ASVs were identified from the soil samples collected at the end of the experiment.Chytridiomycota and Basidiomycota were the most abundant fungal phyla, accounting for 54.0% and 19.7% of the total sequence abundance. The relative abundance of Chytridiomycota increased while that of Basidiomycota decreased in microbe-inoculated soils versus in non-inoculated soils (Fig. 4a). The arbuscular mycorrhizal fungal group Glomeromycota was the fourth most abundant phylum with an averaged relative abundance of 8.1% and they were found exclusively in microbe-inoculated soil. We detected Mucoromycotain leaf inoculum and Glomeromycota in soil inoculum at the beginning of the experiment, which may be the source of fungi in soil samples collected at the end of experiment. The soil bacterial community was dominated by Actinobacteriota and Proteobacteria , accounting for 68.6% and 17.7% of total sequence abundance respectively. The relative abundance of these two phyla was consistent in all soil samples, soil inoculum and the background soil substrate (Fig. 4b).
Inoculation of soil microbes increased soil fungal ASV richness but had no effect on bacterial ASV richness, in contrast, inoculation of leaf microbes decreased soil bacteria ASV richness but showed no influence on fungal ASV richness (Table 3). We also found plant diversity increased the richness of bacterial but not fungal ASVs (Table 3). Both soil inoculation treatment and plant diversity influenced microbial community composition; distance-based redundancy analysis showed significant differences in microbial community composition along plant diversity gradients and between soil inoculation and non-inoculation treatments (Fig. 5), and PERMANOVAs showed that plant diversity and soil inoculation treatment respectively explained 1.7% and 9.6% of the variation in fungal community composition and 2.4% and 12% of the variation in bacterial community composition (Table 4).
We identified 30 bacterial ASVs and 4 fungal ASVs that were significantly more abundant in inoculated soils versus non-inoculated soils. Most of the differentially abundant ASVs belonged to the bacterial genus Streptomyces and fungal genusSpizellomyces (Fig. S2). These taxa along with arbuscular mycorrhizal fungi which were only found in inoculated soils were potentially the causes of soil inoculation effect, leading us to analyzing the diversity and abundance of these particular taxonomic groups. We found that both the richness and abundance of arbuscular mycorrhizal fungi increased when high-concentration leaf microbe inoculum was inoculated and decreased with plant diversity (Table S2), and the richness of Streptomyces decreased with plant diversity (Table S2).