3.3 Autotrophic and nitrogen-fixing bacteria
Based on the Chao1 and the Shannon index, the community diversity of autotrophic bacteria containing cbbL showed the order of bulk soil > rhizosphere soil as well as of high salinity soil > moderate salinity soil = low salinity soil, and the community richness showed similar orders (Figure 3A). In the diversity information analysis, a total of 8 phyla, 11 classes, 28 orders, 32 families, and 59 genera of autotrophic bacteria containing cbbLwere detected, of which the 10 dominant genera wereg_Halorhodospira, g_Marichromatium, g_Thioalkalivibrio, g_unidentified, g_Alkalilimnicola, g_Thiobacillus, g_Rhodovulum, g_Cupriavidus, g_Hydrogenophaga, and g_Ectothiorhodospira . The combined relative abundances of these 10 genera was generally above 90% in all soil samples, with the exception of the CK (58%) and H-NR (83%). The common dominant genera in the bulk soils wereg_Thioalkalivibrio and g_Marichromatium (Figure 3B, E).
In the LEfSe analysis of the autotrophic bacteria containing cbbL(Figure 3G), the statistically significant biomarkers were:o_Chromatiales, o_Rhodospirillales, o_Methylococcales ,o_Thermales, o_Burkholderiales , o_Rhizobiales, o_Synechococcales , o_Gallionellales ando_Rhodobacterales . (Figure 3G).
The community diversity of autotrophic bacteria containing cbbMshowed the order of rhizosphere soil > bulk soil, which was the opposite of autotrophic bacteria containing cbbL(r<-0.6) (Figure 3C, 5). The total of 29 phyla, 47 classes, 94 orders, 138 families, and 276 genera of autotrophic bacteria containingcbbM were detected, with the 10 dominant genera beingunidentified, g_Halothiobacillus, g_Sideroxydans, g_Rhodopseudomonas, g_Thiobacillus, g_Sulfuritalea, g_Leptothrix, g_Magnetospirillum, g_Thiohalomonas, and g_Thiocystis; the sum of the relative abundance of the above 10 genera was around 80% in all soil samples. Dominant genera were g_Halothiobacillus, g_Sideroxydans, g_Rhodopseudomonas , and g_Lepthrix in the rhizosphere soil, whereas g_Halothiobacillus, g_Thiobacillus, g_Sulfuritalea , and g_Thiohalomonas predominated in the bulk soil. In addition, the abundance of g_Thiohororhabdus was lower in the rhizosphere soil (0.44%) than the bulk soil (4.78%) (Figure 3D, F).
In the LEfSe analysis of the autotrophic bacteria containing cbbM(Figure 3H), the statistically significant biomarkers were:o_Nitrospirales, o_Thermales, o_Halobacteriales, o_Chlorobiales, o_Acidithiobacillales, o_Thiotrichales, o_Chromatiales, o_Rhodospirillales, o_Methylococcales, o_Burkholderiales, o_Desulfovibrionales , ando_Pseudonocardiales .
The community diversity of nitrogen-fixing bacteria containing nifH showed the order of rhizosphere soil > bulk soil, which was the opposite of the autotrophic bacteria containing cbbL (r<-0.6) and similar to the autotrophic bacteria containing cbbM (r>0.6) (Figure 4A, 5). Total of 26 phyla, 52 classes, 100 orders, 163 families, and 309 genera containing nifH were detected, with the 10 dominant genera being unidentified, g_Desulfuromonas, g_Geobacter, g_Bradyrhizobium, g_Azoarcus, g_Desulfovibrio, g_Geoalkalibacter, g_Azospirillum, g_Anaeromyxobacter, and g_Sinorhizobium . The relative abundances of these 10 genera were between 61% and 69% in the rhizosphere soil and 71%-76% in the bulk soil and CK. The dominant genera in CK and bulk were g_Desulfuromonas, g_Geoalkalibacter, g_Anaeromyxobacter, g_Pelobacter, g_Desulfobulbus, g_Pseudomonas, g_Ectothiorhodospira, g_Methylomonas, and g_Halorhodospira , whereas the dominat ones in the rhizosphere soil wereg_Geobacter, g_Desulfovibrio, g_Azospirillum, g_Sinorhizobium, g_Pseudacidovorax, g_Nostoc, g_Dechloromonas, g_Paraburkholderia, g_Rubrivivax, and g_Skermanella (Figure 4B, C).
A variety of unique nitrogen-fixing bacteria containing nifH in CK were showed in the LEfSe analysis (Figure 4D) to be statistically significant biomarkers:o_Chromatiales, o_Burkholderiales, o_Bacteroidetes, o_Rhizobiales, o_Oceanospirillales, o_Desulfobacterales, o_Xanthomonadales, o_Enterobacterales , and