Climate change, primarily driven by rising carbon dioxide (CO₂) emissions, represents one of the greatest challenges of our time. Scientists have long assumed that with warming climate, plants and trees will inevitably increase the amount of CO₂ they release into the atmosphere through a process called respiration. This increased release would in turn lead to even more warming, creating a positive feedback loop. But new research suggests that this prediction may not be as dramatic as previously thought.

A study by an international research team, published in the journal Science, finds that the amount of CO₂ released by respiring tree trunks under a warming climate could be significantly less than currently predicted. This means that carbon emissions in a warmer future climate will not increase as sharply as previously thought.

The key to this finding is thermal acclimation of plants – the way plants respond to temperature changes. The research has revealed an important difference between short-term and long-term temperature responses of tree respiration. Short-term changes, measured in seconds, minutes and hours, are rapid and predictable based on enzymatic processes in plant tissues. Most global ecosystem models to date have assumed that this short-term behavior also applies to longer time periods, which is not true.

Long-term changes in respiratory rates, measured over months, years, and decades, behave differently. New findings show that thermal acclimation over the long term dampens positive feedback between climate warming and carbon emissions from plants. This means that trees can adapt to warmer conditions over time by not accelerating their respiration processes as much as one would expect based on short-term responses alone.

The research is based on a large global dataset of wood respiration, which includes thousands of measurements on hundreds of species from all major climate zones of the world. The data come from existing databases, publications and from the study's co-authors. The Global Stem Respiration Dataset (GSRD) after review included measurements from 68 field sites and 187 species, with a total of 4627 observations for global spatial analysis. This large dataset provided scientists with sufficient information to test new theories and confirm that previous models may have overestimated tree stem respiration.

The findings of this study have important implications for how scientists predict global carbon flows in a future climate. They suggest that ecosystems around the world will, to some extent, slow down the trends of increasing atmospheric CO₂This is important information in the context of future climate predictions that expect more frequent and intense extremes such as heat waves, fires and droughts.

Models that do not account for, or incorrectly account for, long-term thermal acclimation of stem respiration can predict significantly higher future CO₂ emissions from trees. A comparison with one such model (CLM5) showed that it predicted the release of approximately 4.9 to 11.9 PgC (petagrams of carbon) of additional CO₂ by 2100 compared to simulations that take into account the new study's findings.

Overall, this research strengthens scientists' understanding of how plants respond to temperature changes and provides important insights for refining predictions of the amount and movement of CO₂ in our ecosystems due to a warming climate. It presents new information about how CO₂ production by plants changes over the long term depending on environmental conditions. Spring

A study published in in the journal Science

Glossary of key terms

• Allometric functions: Mathematical equations describing relationships between body measurements, such as trunk diameter and sapwood area, used to convert between different units.
• CRU TS: A high-resolution gridded climate dataset used to extract temperature data for the various locations in the study.
• DURC (Dual Use Research of Concern): Research that could potentially be misused for harmful purposes. Mentioned in the reproducibility checklist as a point for consideration.
• EIV (Errors-in-Variables) regression: A statistical method used to analyze relationships when both variables are measured with error.
• Embolism: The formation of air bubbles in the xylem of trees, which can disrupt water transport.
• FPAR (Fraction of Photosynthetically Active Radiation): The fraction of incident sunlight that plants use for photosynthesis.
• GPP (Gross Primary Production): The total amount of carbon fixed by plants through photosynthesis.
• GSRD (Global Stem Respiration Dataset): A compiled set of stem respiration measurements from various locations and species, used as a primary data source.
• Growing season: The time of year when environmental conditions (e.g. temperature above 5°C) are suitable for tree growth.
• LAI (Leaf Area Index): Total leaf area per unit of land area, an indicator of vegetation density.
• LMM (Linear Mixed Models): A statistical method used to analyze data that allows for the inclusion of both fixed and random effects.
• MDAR (Materials, Design, Analysis, Reporting): A framework and checklist for ensuring the reproducibility and transparency of scientific research.
• Parenchyma: A type of living cell in wood (including ray and axial parenchyma cells) that is involved in storage, transport, and respiration.
• PFT (Plant Functional Type): Categorization of plants based on common characteristics related to life cycle, leaves, and structure (e.g., evergreen broadleaf trees).
• PPFD (Photosynthetic Photon Flux Density): Photon flux density in the range of photosynthetically active radiation.
• Q₁₀: Thermal sensitivity coefficient, which indicates the factor of increase in process speed when the temperature increases by 10°C.
• Ra (Autotrophic respiration): Total respiration of the plant (including leaves, stems and roots).
• rs (Respiration rate): The rate at which CO₂ is released from the trunk.
• rs.gt: Strain respiration rate standardized to growth temperature (Tg).
• rs25: Respiration rate of the strain standardized to a reference temperature of 25°C.
• Sap flow: The flow of water through the xylem in a tree trunk, driven by transpiration from the leaves.
• Sapwood: Physiologically active part of wood that participates in the transport of water and nutrients and contains living, breathing cells.
• SPLASH model: A model used to simulate hydroclimatic variables such as actual and potential evapotranspiration.
• Stem respiration: The process of releasing CO₂ from a tree trunk.
• Tg (Growth temperature): Average temperature during the growing season with temperatures above 5°C.
• Thermal acclimation: The ability of an organism to adapt its thermal sensitivity to changing temperature conditions over time.
• Transpiration: The process of releasing water vapor from plants into the atmosphere, primarily through stomata.
• TRENDY models: Global biogeochemical models used to simulate carbon fluxes and other processes in the terrestrial biosphere.
• TRY database: Global database of plant traits.
• Upscaling: The process of extrapolating measurements from a smaller scale (e.g., an individual tree) to a larger scale (e.g., a global level).
• VPD (Vapor Pressure Deficit): The difference between the saturated water vapor pressure and the actual water vapor pressure, an indicator of air dryness.
• Wood density: Dry weight of wood per unit volume, an important characteristic for estimating biomass and carbon content.
• Xylem: Tissue in plants responsible for transporting water and nutrients from roots to leaves and for mechanical support.