Landward distribution and association of the soil stable organic carbon fractions and dominant bacterial phyla

Abstract:

[Objective] To explore the landward distribution and association of the soil stable organic carbon (SOC) fractions and dominant bacterial phyla. [Methods] Along the gradient from the long-term flow with no plant (Np) or Juncellus serotinus (Js), seasonal flow with Juncus effusus (Je) and Potentilla anserina (Pa) to long-term no-flow with Leymus chinensis (Lc) and Stipa grandis (Sg), we collected soil samples in wetland and dryland from Xilin River Basin. We detected the content of SOC fractions [fulvic acid (FA), humic acid (HA), and humin (HM)] in different vegetation zones with the method recommended by International Humic Substances Society (IHSS). Meanwhile, we checked the relative abundance of dominant bacterial phyla by high-throughput sequencing of 16S rRNA gene. Furthermore, we analyzed the association between SOC fractions and dominant bacterial phyla based on Pearson’s correlation analysis, redundancy analysis (RDA), variation partitioning analysis (VPA), and structural equation modeling (SEM). [Results] The SOC fractions (FA, HA, HM), Acidobacteria, Actinobacteria, and Gemmatimonadetes demonstrated the landward distribution with an increasing trend, and peaked in the dryland zone from the long-term no-flow area, whereas Bacteroidetes showed the landward distribution with a decreasing trend. As the dominant bacterial phyla in dryland zone from the long-term no-flow area, Gemmatimonadetes, Acidobacteria, and Actinobacteria showed significantly (P<0.05 or P<0.01) positive correlation with HA and HM. As the dominant bacterial phyla in wetland zone from long-term flow and seasonal flow areas, Bacteroidetes had a significantly (P<0.01) negative correlation with FA, HA, and HM. SEM revealed the direct and indirect links between SOC fractions and dominant bacterial phyla. [Conclusion] SOC fractions and dominant bacterial phyla exhibit obvious landward distribution in Xilin River Basin. The increase of soil SOC fractions is associated with the increase of Gemmatimonadetes, Acidobacteria, and Actinobacteria, and the decrease of Bacteroidetes.