A new study published in Science presents compelling evidence that the thermal acclimation of stem respiration plays a critical role in modulating the carbon–climate feedback. Led by LEMONTREE’s Zhang Han and Han Wang of Tsinghua University, it provides the first Eco-Evolutionary Optimality theory-based global analysis of how stem respiration acclimates to rising temperatures—and how this effect could substantially reduce projected carbon losses from terrestrial ecosystems under future climate change scenarios.
While tree trunks may appear static, they are as vital and dynamic as leaves in a plant’s lifecycle. Through ecological and evolutionary optimality theory, we hope to shed new light on trunk respiration—unveiling its hidden significance in shaping plant function and survival. Trees are not just silent giants; every part, from canopy to core, plays a crucial role in nature’s intricate balance.
Zhang Han (Tsinghua University)
Respiration—the process by which plants use oxygen to convert sugars into energy—returns nearly half of all the carbon fixed by photosynthesis back to the atmosphere. While leaf respiration has been widely studied, the contribution of woody stem respiration has been less well understood, even though it represents a large portion of total plant respiration, particularly in forests.
Critically, most climate models assume that plant respiration increases sharply with temperature. While this is true in the short term, plants can acclimate to warming over longer timescales, adjusting their respiratory rates downward. However, the extent of this acclimation—especially in woody stems—has been poorly quantified, and current Earth system models largely overlook it.
The research team tackled this knowledge gap by developing a new eco-evolutionary optimality (EEO) theory, which links stem respiration to the costs of water transport. This model proposes that respiration is tied to the energetic demands of maintaining the water continuum through the stem, which decrease with temperature because warmer water flows more easily. This mechanistic basis allowed them to predict how stem respiration should adjust with warming across both space and time.
The theory yielded two key predictions:
- Respiration measured at a common reference temperature (25°C), known as rs25, should decline by ~10% per degree of warming.
- Respiration at actual growth temperature (rs.gt) should decline by ~2.3% per degree.
To test these predictions, the team assembled the Global Stem Respiration Dataset (GSRD), comprising over 8,782 observations from 187 species across 68 field sites, including 4155 seasonal data, alongside experimental data. They found that rs25 decreased by about 9.8% per degree across spatial temperature gradients—strikingly close to the theoretical value. Similarly, rs.gt decreased by around 1.5% per degree, matching the theory’s prediction within uncertainty bounds.
The findings held across diverse ecosystems, sampling methods, and even in controlled warming experiments, where tree saplings exposed to higher temperatures for a week showed similar reductions in respiration.
Scaling their model globally, they estimated that trees released about 27.4 Pg of carbon per year through stem respiration in 2010. But projections for 2100 reveal a striking result: if respiration acclimation is ignored, stem carbon emissions are overestimated by up to 46% under high-emissions scenarios. That’s equivalent to 24 billion tonnes of carbon—more than double the annual emissions of all human activities today.
Why does this matter? Because many leading Earth system models (ESMs)—including CLM5, CABLE, and QUINCY—either ignore stem-specific acclimation or assume it behaves like leaf respiration. These models tend to use far lower sensitivity values (~−1.8% per K for rs25) than this study shows is appropriate. As a result, current models likely overstate land carbon losses and warming feedback.
The trunks of living tree not only generously lift their leafy arms casting nice shade for us on hot summer days, but also hold promise on mitigating future warming by weakening the positive climate-carbon feedback. With insights drawn from eco-evolutionary optimality, we hope to understand tree trunks, their lives and functions, better better than we had.
-Prof Wang Han (Tsinghua University)
Take-home message
This study provides robust evidence that plants with woody stems thermally acclimate their respiration in ways that substantially reduce carbon losses under climate warming. Accounting for this effect weakens the carbon–climate feedback by tens of gigatonnes of carbon and highlights the need to revise current Earth system models. Trees, it turns out, are smarter breathers than we thought—and incorporating that insight is critical for predicting our planet’s future.
You can read the full paper here:
Zhang, H., Wang, H., Wright, I.J., Prentice, I.C., Harrison, S.P., Smith, N.G., Westerband, A.C., Rowland, L., Plavcová, L., Morris, H., Reich, P.B., Jansen, S., Keenan, T. & Nguyen, N.B. (2025). Thermal acclimation of stem respiration implies a weaker carbon-climate feedback. Science. 388,984-988. 10.1126/science.adr9978