Concept · environmental-science
Carbon cycle
Follow Carbon cycle — see important new research and changes in evidence.Change log
What changed
Dated edits to this page's evidence: studies added or removed from a claim, claims added or withdrawn, and new explanations tagged here. Rewordings are not listed.
- Concept page published
Carbon-cycle studies track how carbon moves through plants, soils, lakes or the atmosphere under environmental change.
It is the biogeochemical core of climate–ecosystem science.
Evidence
What the evidence shows
Drawn from 10 studies in this library. Each finding starts with a plain-language takeaway, then the denser detail. Supports means evidence for a finding; Challenges means evidence against a stated position; Qualifies marks scope with a short note on each study’s contribution. Challenged positions are labeled — they are not findings.
This library holds 10 empirical papers on carbon cycle with measured outcomes rather than reviews.
- Shrubs help warming unlock ancient peat carbon
- Canopy nitrogen and tree carbon uptake
- Shrubs and trees empty subarctic soil carbon
Study Role Design N Population Outcome Shrubs help warming unlock ancient peat carbon Supports OtherFactorial warming × vegetation-removal peatland experiment with 14C-partitioned respiration Treatment-level replicates n=3 for 14C/CO2 sampling; exact plot census not a single primary N in stored text Peatland plots with bare, bryophyte, graminoid, dwarf-shrub, and full vegetation treatments Ecosystem respiration flux and age (14C) under warming and vascular-plant presence Canopy nitrogen and tree carbon uptake Supports Animal / in-vitro15N tracer mesocosm comparing canopy vs soil nitrogen targeting in Sitka spruce Potted Sitka spruce mesocosms; mean aboveground biomass 370 g/tree — exact tree N not primary in stored text Potted Sitka spruce trees Aboveground and wood recovery of canopy-applied vs soil-applied 15N Shrubs and trees empty subarctic soil carbon Supports Cross-sectionalSpace-for-time forest–heath transects comparing SOC and respiration under shrub expansion N=19 · 12 Abisko + 7 Vassijaure forest–heath transects Subarctic treeline heath, shrub, and birch forest plots in northern Sweden Soil organic carbon stocks and respiration rates across vegetation types Vascular plants raised peatland respiration 145% vs bare peat; warming increased fluxes 111% on bare and 63% with dwarf-shrubs and shifted 14C toward older carbon where shrubs were present.
Canopy-applied 15N is recovered aboveground about three times more than soil-applied N.
At a Swedish subarctic treeline, shrub and birch plots stored far less soil organic carbon than nearby heaths and respired that carbon faster, implying woody expansion can accelerate soil C loss.
Across a Swedish stream and two lakes, the most water-loving DOM fractions lost 12–25% of DOC in 150 days versus 6–15% for hydrophobic fractions.
Open questions
Tensions and limits
Some items are genuine disagreements on the same question. Others mark different assays, populations, or outcomes — limits on how far one study travels — not a forced fight between papers.
A mesocosm, a peat profile or a shrub plot does not close the global carbon budget.
Study Role Design N Population Outcome Shrubs help warming unlock ancient peat carbon Supports OtherFactorial warming × vegetation-removal peatland experiment with 14C-partitioned respiration Treatment-level replicates n=3 for 14C/CO2 sampling; exact plot census not a single primary N in stored text Peatland plots with bare, bryophyte, graminoid, dwarf-shrub, and full vegetation treatments Ecosystem respiration flux and age (14C) under warming and vascular-plant presence Canopy nitrogen and tree carbon uptake Supports Animal / in-vitro15N tracer mesocosm comparing canopy vs soil nitrogen targeting in Sitka spruce Potted Sitka spruce mesocosms; mean aboveground biomass 370 g/tree — exact tree N not primary in stored text Potted Sitka spruce trees Aboveground and wood recovery of canopy-applied vs soil-applied 15N
Common misconceptions
More nitrogen always means more stored carbon.
Canopy vs soil uptake, seasonality and vegetation type change the C:N outcome.
Exam-style questions
Short-answer questions that ask you to explain or compare, not recall.
What does carbon cycle mean in this library?
Carbon-cycle studies track how carbon moves through plants, soils, lakes or the atmosphere under environmental change.
Name one empirical finding from the carbon cycle papers.
Vascular plants raised peatland respiration 145% vs bare peat; warming increased fluxes 111% on bare and 63% with dwarf-shrubs and shifted 14C toward older carbon where shrubs were present.
What is a limit of carbon cycle evidence here?
A mesocosm, a peat profile or a shrub plot does not close the global carbon budget.
The studies
10 studies in this library bear on Carbon cycle, ordered by citations. The first 8 are shown.
- Plant diversity builds soil carbon via microbes
Higher plant species richness raises soil organic carbon by boosting microbial growth, biomass, and fungal necromass, not carbon-use efficiency.
- Shrubs and trees empty subarctic soil carbon
At a Swedish subarctic treeline, shrub and birch plots stored far less soil organic carbon than nearby heaths and respired that carbon faster, implying woody expansion can accelerate soil C loss.
- Shrubs help warming unlock ancient peat carbon
Vascular plants raised peatland respiration 145% vs bare peat; warming increased fluxes 111% on bare and 63% with dwarf-shrubs and shifted 14C toward older carbon where shrubs were present.
- Hydrophilic freshwater DOM biodegrades fastest
Across a Swedish stream and two lakes, the most water-loving DOM fractions lost 12–25% of DOC in 150 days versus 6–15% for hydrophobic fractions.
- Arctic food-web carbon is going isotopically light
Across 17 Arctic regions, water-column POC δ13C fell 0.149‰ per year—far faster than DIC/CO2 (0.011‰/yr)—and seal and whale tissues tracked the decline.
- Canopy nitrogen and tree carbon uptake
Canopy-applied 15N is recovered aboveground about three times more than soil-applied N.
- As acid rain fades, climate steers water browning
DOC rose at 383 of 426 northern sites since 1990; early increases tracked falling sulfate, while later increases are nearly half climate-driven.
- Dark lakes change how microbes eat land carbon
In a dark Ontario lake, more aromatic terrestrial organic matter lowered bacterial production and slightly raised CO2.
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- Warm soils change microbes, not Q10 of respiration
Along a >31°C geothermal gradient in New Zealand, bacterial and fungal communities shifted but MMRT temperature-sensitivity of soil respiration showed no thermal adaptation.
- Amazon forest carbon is highly seasonal
An Amazon forest stored about four times more carbon in the dry season than the wet season.
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