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Faster-and-tighter nitrogen cycle supports mature forest productivity under elevated CO2
Manon Rumeau1,2, Carolina Mayoral1,2, Fotis Sgouridis3
1Birmingham Institute of Forest Research, University of Birmingham, Birmingham B15 2TT, UK.
Science Advances
|July 29, 2026
Summary
Elevated atmospheric carbon dioxide (CO2) boosts forest growth by increasing nitrogen (N) availability through enhanced N mineralization. This suggests forests can adapt to higher CO2 levels, but long-term N supply may be limited.
Area of Science:
- Forest Ecology
- Biogeochemical Cycles
- Climate Change Research
Background:
- Rising atmospheric carbon dioxide (CO2) concentrations are expected to increase forest carbon (C) uptake.
- Nitrogen (N) availability is often considered a limiting factor for forest productivity under elevated CO2.
- Previous studies showed significant biomass gains in a mature oak forest under Free Air CO2 Enrichment (eCO2).
Purpose of the Study:
- To investigate if changes in soil nitrogen (N) fluxes explain the observed biomass gains in an oak forest under eCO2.
- To understand the mechanisms of N cycling adaptation in forest ecosystems exposed to elevated CO2.
Main Methods:
- Conducted a 6-year Free Air CO2 Enrichment (eCO2) experiment in a mature oak forest.
- Measured in situ net and gross nitrogen (N) fluxes, including ammonification and nitrification.
- Assessed changes in fine root biomass and soil respiration in response to eCO2.
Main Results:
- Enhanced N mineralization and ecosystem N conservation were observed, supporting increased forest productivity under eCO2.
- In situ net and gross N ammonification rates increased by approximately 30%, particularly during oak budburst.
- Higher N ammonification correlated with increased fine root biomass and soil respiration, while gross nitrification decreased.
Conclusions:
- Forest nitrogen cycling can adapt to support increased carbon (C) uptake under elevated CO2 (eCO2) through enhanced N availability.
- Plant-soil interactions facilitate a faster-yet-tighter N cycle, promoting productivity.
- Long-term C uptake capacity may be limited by soil organic N stocks and reduced anthropogenic N deposition.
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