A group from Gansu Gaolan Field Scientific Observation and Research Station for Agricultural Ecosystem, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China, etc. has reported that the combined application of a bacterial inoculant and sucrose can improve the growth and quality of Rheum palmatum suppressing pathogen Fusarium spp.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8835959/
There are many bacterial and fungal species that can function as (plant growth-promoting microbes) PGPM, of which Bacillus members are well-described in the literature for successfully promoting plant growth in diverse ways. Bacillus isolates colonize host plant roots and promote plant growth by producing bio compounds, such as the hormone indole-3-acetic acid (IAA), as well as spermidine and 2,3-butanediol, by defending against pests and pathogens by producing antibiotic substances such as hydrogen cyanide (HCN), chitinase, and siderophores.
In general, soil is usually a carbon-limited state, and less than 5% of total bacteria are in an active state under such conditions. Carbon sources, especially the most common sucrose, could impact bacteria as a direct energy source for growth. So, in this work, it was evaluated how Baillus spp. respond to the small molecular carbon addition such as sucrose and their co-effects on the rhizosphere microecology.
The combinations of three concentrations of Bacillus amyloliquefaciens EZ99 inoculant (1.0 × 105, 1.0 × 106, and 1.0 × 107 colony-forming units (CFU)/mL, denoted as LB, MB, and HB, respectively) and with three sucrose concentrations (0.15, 1.5, and 15 g/L, denoted as LS, MS, and HS, respectively) were evaluated on R. palmatum growth and yield.
Although the HB treatment increased the growth of R. palmatum (plant length, crown weight, leaf length, and leaf weight) comparing with control (CK), it decreased the growth when coupled with sucrose, especially under the highest concentration of sucrose (HS). This indicates that a high level of bacterial inoculant (1.0 × 107 CFU/mL) amended with a high level of sucrose (15 g/L) suppressed the plant growth-promoting function of PGPM. And, further, the fresh weight of R. palmatum roots were the most significantly improved under the LB + LS and LB + MS treatments (see below)
Typical differences observed in the comparisons are as follows:
- Eight kinds of anthraquinones, the major constituents of rhubarb, were differentially identified in the comparisons. The LB + LS group accumulated the highest level of aurantio-obtusin-6-O-glucoside and torachrysone-8-O-glucoside, but reduced levels of torachrysone and laccaic acid D, while the rhubarbs under the LB treatment accumulated only 2-acetoxymethyl-anthraquinone.
- The co-effects of PGPM and sucrose in the LB + LS treatment did not lead to a significant net difference in the total contents of soil nutrients, but they significantly increased the contents of total potassium which could mediate the bioavailability of potassium and nutrients’ cycling in the soil.
- As for rhizobacteria community, sucrose addition had little impact on bacterial community structure in LS soil, yet it modulated the diversity induced by the PGPM addition in LB + LS soil.
- As for fungal community, the Ascomycota and Mortierellomycota were the two most abundant phyla, together accounting for more than 92.5% of the relative abundance of the total fungal sequences. The most abundant phylum Ascomycota was enriched the most in CK (79.1%), and diminished the most in LB + LS (71.6%) treatment. At the genus level, compared with CK, the first dominant genus Fusarium was decreased, whereas the second dominant genus Mortierella was increased in all treatments, with the highest increase recorded in the LB + LS treatment.