Abstract:
To probe into the impacts of organ cadmium accumulation on endophytic bacteria in
Blumea balsamifera, the methods of high-throughput sequencing of 16S rRNA gene V3-V4 region
and molecular ecological network analysis were employed to study the effects of Cd accumulation
in roots, stems and leaves of B. balsamifera on the community characteristics of endophytic
bacteria under different exogenous cadmium treatments (0 and 2.0 mg·kg-1). The results were as
follows: (1) In comparison with the control group without exogenous cadmium addition (0 mg·kg-
1, Cd0), the treatment group with cadmium spiking in soils (2.0 mg·kg-1, Cd2) promoted plant growth and the cumulative Cd contents in root, stem and leaf, with the order of leaf (16.75 mg·kg-
1) > stem (11.99 mg·kg-1) > root (3.96 mg·kg-1). (2) Alpha diversity analysis showed that the
endophytic bacteria richness (Sobs, Ace and Chao indices) and diversity (Shannon and Simpson
indices) for organs were the highest in roots, followed by stems and leaves under Cd0 and Cd2
treatments. Additionally, the indices of richness and diversity of endophytic bacteria for each
organ under Cd2 treatment were superior to those under Cd0. (3) At the phylum level,
Proteobacteria, Actinobacteriota and Firmicutes were the dominant bacterial phyla in all the
organs for both treatments; At the genus level, Delftia was the main bacterial genus with the
relative abundance ranged from 53.0% to 92.7% and 57.1% to 89.2% in the plant organs of Cd0
and Cd2, respectively; Certain similarities existed among the endophytic bacterial community
structures of roots, stems and leaves of B. balsamifera, and Cd2 increased the proportion of
mutual endophytic bacterial genera in roots, stems and leaves and that of unique endophytic ones
in each organ (except the root). (4) LDA Effect Size analysis showed that there existed the
differences on endophytic bacterial genera residing in different organs within a group and also the
same organ between groups. (5) Redundancy analysis (RDA) showed that the contents of
rhizosphere soil Cd and plant organ Cd were significantly correlated with the composition of
endophytic bacterial community. (6) Co-occurrence network analysis clarified that cadmium
accumulation in B. balsamifera complicated the interaction network of endophytic bacteria
occurring in root and leaf, and enhanced the competition among endophytic bacterial species in
root and stem, and the symbiosis in leaf. In summary, exogenous Cd treatment affected the
community structure and interaction mode of endophytic bacteria in B. balsamifera organs.