Landward differentiation characteristics of anoxygenic photosynthetic bacterial populations and their influencing factors in Xilin River Basin

Abstract:

[Objective] This study aimed to elucidate the landward differentiation characteristics of potential anoxygenic photosynthetic bacteria (AnPB) and their influencing factors in Xilin River Basin. [Methods] Soil samples were collected along a landward gradient from the turbulent flow zone with no plant (Np), sluggish flow zone with Juncellus serotinus (Js) and stagnant flow zone with bacterioplankton (Pb) in riverbed, the riparian zones including semi-aquatic (hygrophytic) Juncus effusus (Je) and semi-xerophytic (hygrophytic) Potentilla anserina (Pa) to terrace zones including xerophytic Leymus chinensis (Lc) and Stipa grandis (Sg). The database for AnPB at family level wasestablished based on literature informatics. In addition, landward differentiation of potential AnPB populations at family level and their relative abundance was analyzed by 16S rRNA gene high-throughput sequencing. Furthermore, the environmental influence of physicochemical factors on landward differentiation of potential AnPB was studied based on Pearson correlation analysis, redundancy analysis (RDA), multivariate regression tree (MRT) and structural equation modeling (SEM). [Results]Purple sulfur bacteria (Ectothiorhodospiraceae) and purple non-sulfur bacteria (Rhodobacteraceae, Rhodocyclaceae,Acetobacteraceae, Comamonadaceae and Holophagaceae) populations were mainly distributed in aquatic and semi-aquatic (hygrophytic) habitats, whereas purple non-sulfur bacteria (Rhodospirillaceae, Bradyrhizobiaceae, Hyphomicrobiaceae and Rhodobiaceae), Gemmatimonadaceae, Acidobacteriaceae and green non-sulfur bacteria (Roseiflexaceae) populations were mainly distributed in semi-xerophytic (hygrophytic) and xerophytic habitats. Herein, the relative abundance of the potential AnPB populations in aquatic and semi-aquatic (hygrophytic) habitats showed positive correlation with moisture content (P<0.05 or P<0.01), while that in semi-xerophytic (hygrophytic) and xerophytic habitats was positively correlated with salinity and total nitrogen content (P<0.05 or P<0.01). MRT analysis indicated that the total explanation of salinity, moisture and total nitrogen for the landward differentiation of the potential AnPB populations was 62.39%, 14.01%, and 12.68%, respectively. SEM revealed the positively direct links between salinity and Rhodocyclaceae as well as between moisture/TN and Rhodobacteraceae. [Conclusion] The landward differentiation of potential AnPB populations in Xilin River Basin is clear. Salinity, moisture and total nitrogen are main environmental factors directly or indirectly co-driving the landward differentiation. This study contributes to a better understanding of the biodiversity and ecosystem function of AnPB community in Xilin River Basin, and also underpins the implementation of an innovative strategy for reducing atmospheric carbon dioxide concentration and increasing soil carbon sequestration.