Research report: Rhizosphere microbial community structure in the water-level-fluctuation zone under distinct waterlogging stresses

A March 2023 field study in the Three Gorges Reservoir’s water-level-fluctuation zone found that bacterial and fungal diversity was generally higher in rhizosphere and nearby non-rhizosphere soils associated with stronger waterlogging stress. The observational study examined Rumex acetosa L. and Oxybasis glauca at the Tangjiatuo section in Jiangbei District, Chongqing, China. Researchers designated sites above 165 m as a high-elevation area with weak waterlogging stress and sites below 165 m as a low-elevation area with strong stress.

They collected rhizosphere soil from more than 20 individuals of each plant in each category, along with nearby non-rhizosphere soil. Three separate samples were collected for each soil type. High-throughput sequencing targeted bacterial 16S and fungal ITS regions, while 14 soil physicochemical and enzyme-activity indicators were measured.

The analysis detected 38,517 bacterial operational taxonomic units across 63 phyla and 518 genera, and 8,658 fungal OTUs across 15 phyla and 652 genera. Five alpha-diversity measures generally indicated greater richness and diversity under stronger waterlogging for both soil types associated with each plant. For R. acetosa, the reported rhizosphere Chao1 richness values were 3,433.82 ± 76.86 under weak stress and 3,676.56 ± 601.87 under strong stress.

Plant differences were clearer under weak stress than under strong stress. Rhizosphere bacterial Chao1 values under weak stress were 3,433.82 ± 76.86 for R. acetosa and 2,591.31 ± 882.75 for O. glauca. Under strong stress, the respective values were closer at 3,676.56 ± 601.87 and 3,549.41 ± 715.35.

Proteobacteria was the dominant bacterial phylum in samples associated with both plants, while Ascomycota led most fungal communities despite substantial variation among samples. In R. acetosa rhizosphere soil, Ascomycota represented 53.8% under strong stress, while Chytridiomycota, Glomeromycota and Rozellomycota together accounted for nearly 28%. In weak-stress O. glauca rhizosphere soil, Ascomycota represented about 60%, compared with 16.14% for Mortierellomycota and 17.00% for Chytridiomycota.

Linear discriminant analysis identified more fungal than bacterial biomarkers. R. acetosa had three fungal biomarkers in weak-stress rhizosphere soil, compared with 13 in strong-stress non-rhizosphere soil and 10 in strong-stress rhizosphere soil. O. glauca had three in strong-stress rhizosphere soil, five in weak-stress non-rhizosphere soil and 10 in strong-stress non-rhizosphere soil.

Bacterial biomarkers were less widespread, but weak-stress R. acetosa rhizosphere soil contained Bacteroidetes, Gammaproteobacteria and Ramlibacter. PICRUSt2 produced predicted rather than directly measured metabolic profiles. Aerobic respiration I, pathway PWY-3781, represented about 1.5% of predicted bacterial pathways, and stronger waterlogging had little effect on the relative abundance of the 10 leading predicted bacterial pathways.

PWY-3781 and aerobic respiration II in yeast, PWY-7279, were leading predicted fungal pathways across the tested soils. Redundancy analysis associated R. acetosa bacterial and fungal community variation with electrical conductivity and pH. The first two bacterial ordination axes explained 34.25% and 16.58% of relative-abundance variance, respectively.

For O. glauca, bacterial structure was associated with nitrate nitrogen, total ammonium nitrogen and several enzyme activities, while fungal structure was associated with electrical conductivity, a nitrogen variable, total nitrogen and urease activity. The study was limited to one reservoir section, two plant species and a single March sampling campaign. Because waterlogging intensity was classified by elevation, the categories may also reflect spatial or environmental differences.

The findings therefore show associations rather than causation, and predicted metabolic potential does not establish that inferred pathways were active in the sampled soils.

Subject of Research: Association of waterlogging intensity with rhizosphere and non-rhizosphere microbial diversity in two dominant plants in the Three Gorges Reservoir

Article Title: Rhizosphere microbial community structure in the water-level-fluctuation zone under distinct waterlogging stresses

Article References: Zhou, L., Wu, S., Ma, M., Zou, H., Huang, J., & Yang, J. (2024). Rhizosphere microbial community structure in the water-level-fluctuation zone under distinct waterlogging stresses. One Ecosystem, 9, Article e133645. https://doi.org/10.3897/oneeco.9.e133645

Image Credits: AI Generated

DOI: 10.3897/oneeco.9.e133645

Keywords: Three Gorges Reservoir, waterlogging stress, rhizosphere microbiomes, microbial diversity, Rumex acetosa, Oxybasis glauca, bacterial communities, fungal communities, soil ecology, Rhizosphere, microbial, community