Bacterial composition reflects fine-scale salinity changes while phylogenetic diversity exhibits a strong salt divide
Bibliographic record
Abstract
ABSTRACT Climate change induced salinization events are predicted to intensify and lead to increased salt stress in freshwater aquatic ecosystems. As a consequence, formerly distinct abiotic conditions and associated biotic communities merge, and the emergence, loss, and persistence of microbial taxa modify the types and rates of ecosystem processes. This study examined how bacterial taxonomic and phylogenetic diversity and ecosystem function respond to acute salinization events where freshwater and estuarine communities and environments coalesce. We hypothesized that when the salinity change outpaces microbial adaptation or saline microbial populations are not yet established in formerly freshwater conditions, then these aquatic communities will exhibit diminished carbon cycling rates, decreased microbial diversity, and altered composition of microbial communities compared to historically freshwater communities. We used an experimental mesocosm approach to determine how salinity and the merging of distinct communities influenced resultant bacterial community structure and function. Each mesocosm represented different salinities (0, 5, 9, 13 psu). Two dispersal treatments, representing aquatic communities sourced from brackish 13 psu ponds and a mix of 13 psu and freshwater ponds, were added to all salinity levels and replicated four times. Results revealed that salinity, but not dispersal, decreased bacterial taxonomic and phylogenetic diversity. Carbon mineralization rates were highest in freshwater conditions and associated to bacterial taxa represented in low relative abundance. Acute salinity changes, such as localized flooding due to storm surge, will more negatively affect freshwater aquatic communities compared to chronic exposure to salinization where the communities have had time to adapt or turnover. IMPORTANCE STATEMENT Climate change induced salinization results in the mixing of formerly distinct environmental conditions and aquatic communities. This study examined the consequence of short-term, acute salinity stress on aquatic bacterial taxonomic and phylogenetic diversity and ecosystem function using an experimental approach. Results revealed that salinity, but not the source of aquatic communities, decreased bacterial taxonomic and phylogenetic diversity. Carbon mineralization rates, which represented ecosystem function, were highest in freshwater conditions and also associated with indicator bacterial taxa in low abundance relative to the total microbial community. Taken together, acute salinity changes will more negatively affect freshwater aquatic communities compared to chronic exposure to salinization where the communities have had time to adapt or turnover resulting in recovered biogeochemical functions.
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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".