Field Site-Specific Effects of an Azospirillum Seed Inoculant on Key Microbial Functional Groups in the Rhizosphere
Open Access
- 26 January 2022
- journal article
- research article
- Published by Frontiers Media SA in Frontiers in Microbiology
- Vol. 12, 760512
- https://doi.org/10.3389/fmicb.2021.760512
Abstract
The beneficial effects of plant growth–promoting Rhizobacteria (PGPR) entail several interaction mechanisms with the plant or with other root-associated microorganisms. These microbial functions are carried out by multiple taxa within functional groups and contribute to rhizosphere functioning. It is likely that the inoculation of additional PGPR cells will modify the ecology of these functional groups. We also hypothesized that the inoculation effects on functional groups are site specific, similarly as the PGPR phytostimulation effects themselves. To test this, we assessed in the rhizosphere of field-grown maize the effect of seed inoculation with the phytostimulatory PGPR Azospirillum lipoferum CRT1 on the size and/or diversity of selected microbial functional groups important for plant growth, using quantitative polymerase chain reaction and/or Illumina MiSeq metabarcoding. The functional groups included bacteria able to fix nitrogen (a key nutrient for plant growth), producers of 1-aminocyclopropane-1-carboxylate (ACC) deaminase (which modulate ethylene metabolism in plant and stimulate root growth), and producers of 2,4-diacetylphloroglucinol (an auxinic signal enhancing root branching). To test the hypothesis that such ecological effects were site-specific, the functional groups were monitored at three different field sites, with four sampling times over two consecutive years. Despite poor inoculant survival, inoculation enhanced maize growth. It also increased the size of functional groups in the three field sites, at the maize six-leaf and flowering stages for diazotrophs and only at flowering stage for ACC deaminase and 2,4-diacetylphloroglucinol producers. Sequencing done in the second year revealed that inoculation modified the composition of diazotrophs (and of the total bacterial community) and to a lesser extent of ACC deaminase producers. This study revealed an ecological impact that was field specific (even though a few taxa were impacted in all fields) and of unexpected magnitude with the phytostimulatory Azospirillum inoculant, when considering microbial functional groups. Further methodological developments are needed to monitor additional functional groups important for soil functioning and plant growth under optimal or stress conditions.Funding Information
- Agence Nationale de la Recherche
This publication has 88 references indexed in Scilit:
- Identification of six differentially accumulated proteins of Zea mays seedlings (DKB240 variety) inoculated with Azospirillum brasilense strain FP2European Journal of Soil Biology, 2013
- Microbial Inoculants and Their Impact on Soil Microbial Communities: A ReviewBioMed Research International, 2013
- Monitoring of the relation between 2,4-diacetylphloroglucinol-producing Pseudomonas and Thielaviopsis basicola populations by real-time PCR in tobacco black root-rot suppressive and conducive soilsSoil Biology and Biochemistry, 2013
- Plant growth-promoting rhizobacteria and root system functioningFrontiers in Plant Science, 2013
- Benzoxazinoids in Root Exudates of Maize Attract Pseudomonas putida to the RhizospherePLOS ONE, 2012
- Microbial control over carbon cycling in soilFrontiers in Microbiology, 2012
- Greengenes, a Chimera-Checked 16S rRNA Gene Database and Workbench Compatible with ARBApplied and Environmental Microbiology, 2006
- Ethylene: A Gaseous Signal Molecule in PlantsAnnual Review of Cell and Developmental Biology, 2000
- Stimulation of the ionic transport system in Brassica napus by a plant growth-promoting rhizobacterium (Achromobacter sp.)Canadian Journal of Microbiology, 2000
- Initiation of root growth stimulation by Azospirillum lipoferum CRT1 during maize seed germinationCanadian Journal of Microbiology, 1999