Composition and abundance of soil microbiome
The Illumina analysis generated a total of 39,52,344 bacterial and 21,89,062 fungal sequences with satisfactory average GCQ20 values of 55.42% and 98.96% respectively (Appendix S3: TableS1). These sequences were classified into 1959 and 2475 operational taxonomic units (OTUs) respectively with a similarity threshold of ≥ 97%. Individual rarefaction curves of all the samples reached saturation showing a typical plateau formation for the OTUs detected, thereby indicating sufficient sampling effort (Appendix S2: Fig. S1). Taxonomically, the 1959 identified bacterial OTUs belong to 23 phyla classified under 73 classes, 105 orders, 126 families, 128 genera and 152 species. Similarly, the 2475 identified fungal OTUs represent 13 phyla, 49 classes, 116 orders, 210 families, 401 genera and 589 species.
The bacterial community was dominated by Proteobacteria which ranged from 22.19% in KD_UN to 27.75% in KZ_IN plots and differed significantly between the plots (F1, 16 = 854.649,p < 0.0001) and among the sites (F3, 16= 326.205, p < 0.0001) (Appendix S3: Table S2). Across the sites, phylum Actinobacteria ranged from 12.90% in KZ_IN to 19.96% in KU_UN plots and showed slightly higher abundance in uninvaded (16.3%) as compared to invaded plots (15.3%). Similarly, other phyla that showed different ranges of abundance with significant p -values between the plots and among the sites along the altitudinal gradient are given in Appendix S3: Table S2. The relative abundance in different phyla ranged as follows: Planctomycetes: 13.64% in KU_UN to 20.22% in KZ_UN plots, Verrucomicrobia: 6.77% in KZ_UN to 19.34% in KU_UN plots, Bacteroidetes: 8.08% in TM_UN to 13.46% in KD_IN plots, Acidobacteria: 7.48% in KZ_UN to 11.15% in TM_UN plots, and Chloroflexi: 3.21% in KU_UN to 5.67% in KD_IN plots (Fig. 2a). Fungal community was dominated by Ascomycota forming 53% and 60% in invaded and uninvaded samples respectively. The relative abundances differed significantly between the plots (F1, 16 = 52.373, p < 0.0001) and among the sites (F3, 16 = 48.838, p < 0.0001) along the altitudinal gradient (Appendix S3: Table S2). The abundance of other fungal phyla with significant p -values between plots and among sites along the altitudinal gradient is given in Appendix S3: Table S2. The abundance of Basidiomycota ranged from 6.0% in KZ_UN to 36% in KU_IN plots. Similarly, other phyla such as Mortierellomycota, Mucoromycota, Chytridiomycota, Glomeromycota and Rozellomycota showed different abundance patterns between the invaded and uninvaded plots across the sites (Fig. 2b). The detailed results of abundance profiles of both bacteria and fungi at other taxonomic levels (classes, orders, families, genera and species) are given in Appendix S1: S1 to S5 and Appendix S1: Figures S1-S6.