The potential biofertilization effect of H<sub>2</sub> is accompanied by a modest impact on the composition of microbial communities in the rhizosphere of common vetch
Bibliographic record
Abstract
Background N2-fixing nodules release molecular hydrogen (H2) in the rhizosphere of legumes. The process activates H2-oxidizing bacteria (HOB) in soil, leading to multiple effects on biogeochemical processes and a potential biofertilization effect. The legacy effect of the energy potential of H2 on the soil microbial community structure and the population density of HOB has received little attention. The aim of the current study is to evaluate how the legacy effect of HOB, previously activated in soil microcosms exposed to elevated H2 concentrations (eH2), affects biomass production yield of common vetch (Vicia sativa), the abundance of HOB, and the composition of the rhizosphere microbiome. Methods Contrasting soil samples displaying more than 60% difference in H2 oxidation activity were used as growth substrate for vetch. Soil microbial community composition and diversity were examined by bacterial 16S rRNA polymerase chain reaction (PCR) amplicon sequencing, and dry weight (DW) of the above- and below-ground biomass of vetch was analyzed to assess the impact of HOB enrichment on plant growth. The population density of high-affinity HOB was estimated by using the droplet digital polymerase chain reaction (ddPCR) technique to target the hhyL gene, encoding for the large subunit of group 1H/5 [NiFe]-hydrogenase. Results The abundance of HOB possessing group 1H/5 [NiFe]-hydrogenase was indistinguishable between the treatments, indicating that soil nutrient content (inorganic and organic carbon) and the energy potential of H2 were insufficient to support their growth. Aeromicrobium spp. and Ramlibacter spp. were favored by eH2 exposure at the activation stage, but their response was lost after vetch growth. The root biomass and the root/shoot ratio were reduced in soil conditioned with eH2 compared to control soil exposed to ambient H2, suggesting that the plant growth-promotion activity of HOB reduces root proliferation for nutrient prospection. These results provide new experimental evidence suggesting the biofertilization effect of H2 is not universal and requires specific conditions that are yet to be identified.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".