Evaluating the comprehensive role of endophytic nitrogen-fixing bacteria in sustaining the growth of boreal forest trees on nutrient-poor soils
Bibliographic record
Abstract
West Chilcotin region located in the Sub-Boreal Pine-Spruce xeric-cold biogeoclimatic zone of British Columbia is characterized by cold climate, low annual precipitation and weakly developed soils. Lodgepole pine and hybrid white spruce comprise the most common tree stands in this region. Soils examined from pine and spruce stands revealed that they have poor physico-chemical health and limited plant-available nutrients, particularly nitrogen. Despite the severely nitrogen-limited soils, the continued, vigorous growth of pine and spruce trees is a major conundrum. A rarely evaluated but possible nitrogen-input could be through endophytic diazotrophic bacteria – nitrogen-fixing bacteria living inside plant tissues. Examining this possibility, 55 and 48 bacterial strains were isolated on nitrogen-free media from internal tissues of pine and spruce, respectively, of which 23 and 18 strains showed positive nitrogenase activity. Six strains each from pine and spruce that showed highest nitrogenase activity were evaluated for their effects on their original host as well as the other tree species (i.e., spruce bacteria tested with pine and pine bacteria tested with spruce) in greenhouse trials. All strains colonized both pine and spruce and performed similarly well in both hosts, contributing 15-56% of host’s foliar nitrogen from the atmosphere after one year and significantly enhancing seedling length and biomass. These strains also possess several other plant-growth-promoting abilities such as inorganic and organic phosphate solubilization, IAA production, ACC deaminase activity, siderophore production and lytic enzyme activity. Notably, four strains closely related to the genus Burkholderia – Caballeronia sordidicola LS-S2r and HP-S1r, Caballeronia udeis LP-R2r and Paraburkholderia phytofirmans LP-R1r – provided up to 5.5mg nitrogen per kg tissue to their host after one year, enhanced seedling biomass by up to 7-fold in 18 months and showed significant potential in the aforementioned plant-growth-promoting mechanisms. Therefore, the ability of such highly effective endophytic diazotrophic bacteria to form beneficial ecological associations with pine and spruce trees could explain their sustained growth on extremely nutrient-limited soils of the West Chilcotin region. Furthermore, their effectiveness with a foreign host indicates the lack of plant x microbe specificity, raising the possibility of their utilization as potential biofertilizers to regenerate trees in disturbed and nutrient-poor ecosystems.
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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) | 0.000 | 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".