Response of the microbial community to phosphate-solubilizing bacterial inoculants on Ulmus chenmoui Cheng in Eastern China

Abstract

Phosphate-solubilizing bacteria (PSB) have beneficial effects on plant health and soil composition. To date, studies of PSB in soil have largely been performed under field or greenhouse conditions. However, less is known about the impact of introducing indigenous PSB in the field, including their effects on the local microbial community. In this study, we conducted greenhouse and field experiments to explore the effects of the addition of indigenous PSB on the growth of Chenmou elm (Ulmus chenmoui) and on the diversity and composition of the bacterial community in the soil. We obtained four bacterial isolates with the highest phosphate-solubilizing activity: UC_1 (Pseudomonas sp.), UC_M (Klebsiella sp.), UC_J (Burkholderia sp.), and UC_3 (Chryseobacterium sp.). Sequencing on the Illumina MiSeq platform showed that the inoculated PSB did not become the dominant strains in the U. chenmoui rhizosphere. However, the soil bacterial community structure was altered by the addition of these PSB. The relative abundance of Chloroflexi decreased significantly in response to PSB application in all treatment groups, whereas the populations of several bacteria, including Proteobacteria and Bacteroidetes, increased. Network analysis indicated that Chloroflexi was the most strongly negatively correlated with Proteobacteria, whereas Proteobacteria was strongly positively correlated with Bacteroidetes. Our findings indicate that inoculation with PSB (UC_1, UC_M, UC_J, and UC_3) can improve the growth of U. chenmoui and regulate its rhizosphere microbial community. Therefore, inoculation with these bacterial strains could promote the efficient cultivation and production of high-quality plant materials.

Fig 1. Colony morphology of the four isolates (UC_1, UC_M, UC_J, and UC_3) (a); Phylogenetic tree of the four PSB based on their 16S rRNA gene sequences (b).

Abbreviations: UC_J (Burkholderia sp), and UC_3 (Chryseobacterium sp).

Fig 2. Relationship between phosphorus kinetics and pH changes in response to Pseudomonas synxantha (UC-1) (a) and Enterobacter aerogenes (UC-M) (b).

Fig 3. Effects of four phosphate-solubilizing bacteria on the growth of Ulmus chenmoui Cheng in the greenhouse.

(a) Seedlings inoculated with bacteria on the 1st day; (b) Seedlings inoculated with bacteria on the 90th day. (c) Height of U. chenmoui seedlings. (d) Ground diameter of U. chenmoui. Field trial of the effects of the four PSB on seedling height (e) and ground diameter (f) of U. chenmoui Cheng.

Fig 4. Effects of PSB treatment on plant soil microbiota richness in U. chenmoui.

(a) Venn diagram of four PSB treatments and the CK; (b) Principal components analysis (PCA) analysis of bacteria community in the CK, UC_1, UC_M, UC_J, and UC_3. Symbols on the ordination plot reflect relative dissimilarities in community structures. The variation in microbial community structures explained by each PCA axis is given in parentheses.

Fig 5. Effects of PSB treatment on plant soil microbiota richness in U. chenmoui.

(a) Relative abundances (%) of the top 13 bacterial phyla present in the five groups. (b) Heatmap depicting the results of hierarchical clustering analysis of the abundance of the main genera in the five different rhizosphere soils. Color intensity of the scale indicates the relative abundance of each OTU read. (c) Co-occurrence networks based on the rhizosphere structural communities of U. chenmoui plants. Each node corresponds to an OTU, and edges between nodes correspond to positive (red) or negative (green) correlations inferred from OTU abundance profiles using the SparCC method (pseudo p < 0.05, correlation values < − 0.5 or > 0.5).