Journal Article

Global Photosynthesis Acclimates to Rising Temperatures Through Predictable Changes in Photosynthetic Capacities, Enzyme Kinetics, and Stomatal Sensitivity

Gessler, Arthur, Schneider, Pascal D., Stocker, Benjamin D.

2025

Overview

Thermal acclimation of photosynthesis, the physiological adjustment to temperature over weeks, may help plants mitigate adverse impacts of global warming, but is often under‐represented in Earth System Models (ESMs). We evaluated a plant functional type (PFT)‐agnostic, optimality‐based model of C3 ${\\mathrm{C}}_{3}$ photosynthesis with a global data set of leaf gas exchange measurements. We investigated how three key photosynthesis traits vary along a gradient of growing‐season temperatures Tgrowth $\\left({T}_{\\text{growth}}\\right)$: optimal photosynthesis temperature Topt $\\left({T}_{\\text{opt}}\\right)$, net photosynthesis rate at Topt ${T}_{\\text{opt}}$ Aopt $\\left({A}_{\\text{opt}}\\right)$, and the width of the temperature response curve Tspan $\\left({T}_{\\text{span}}\\right)$. We analyzed how each trait is influenced by three acclimation processes: acclimation of photosynthetic capacities (carboxylation, electron transport, and respiration), their enzymatic responses, and stomatal sensitivity to vapor pressure deficit. The inclusion of all three acclimation processes was essential for reproducing observed patterns: a linear increase in Topt ${T}_{\\text{opt}}$ with Tgrowth ${T}_{\\text{growth}}$, and no correlations of Aopt ${A}_{\\text{opt}}$ and Tspan ${T}_{\\text{span}}$ with Tgrowth ${T}_{\\text{growth}}$. Acclimation of enzymatic responses and stomatal sensitivity was crucial for accurately predicting Topt ${T}_{\\text{opt}}$ and Tspan ${T}_{\\text{span}}$. Acclimation of the photosynthetic capacities was necessary to avoid a bias in Aopt ${A}_{\\text{opt}}$ that can arise when relying on static, PFT‐specific parameters. Comparing a model with all and a model without any acclimation processes showed that thermal acclimation buffers the response of photosynthesis to warming substantially, leading to smaller increases in photosynthesis in cold climates (+2% instead of +18%) and smaller declines in warm climates (−4% instead of −22%). Our observations‐constrained photosynthesis predictions suggest an important role of thermal acclimation in ESM, partly mitigating adverse effects of a warming climate. Plain Language Summary Plants adjust their photosynthetic apparatus in response to gradual temperature changes over weeks, a mechanism known as thermal acclimation. This acclimation may help plants mitigate the impacts of global warming, but many models that predict the response of vegetation to a changing climate often under‐represent it. In this study, we tested a photosynthesis model that predicts a plant's response to gradual temperature changes based on general principles rather than specific plant types. These principles, stemming from optimality theory and fundamental biochemistry, describe thermal acclimation through different internal processes that regulate the use of carbon, water, and energy. We compared the model with a global data set of leaf measurements to disentangle the influence of these processes on photosynthesis. We found that to accurately predict observed patterns, it was essential to include three acclimation processes: adjustments in photosynthetic capacities, enzyme activities, and stomatal response. The model showed that thermal acclimation buffers plants against the effect of global warming, leading to smaller increases in photosynthesis in cold climates and smaller declines in warm climates compared to models without acclimation. This study highlights the importance of incorporating thermal acclimation into vegetation models to improve predictions of plant responses under future climate scenarios. Key Points Thermal acclimation of C3 ${\\mathrm{C}}_{3}$ photosynthesis is predictable across species and climates using optimality theory and fundamental biochemistry Combined acclimation of photosynthetic capacities, enzyme activity, and stomatal response was critical to capture observations Thermal acclimation buffers photosynthesis against warming, reducing increases in cold climates and limiting declines in hot climates

• Publisher: John Wiley & Sons, Inc
• Subject: Acclimation / Acclimatization / Carbon cycle / Carbon sequestration / Carboxylation / Climate change / Cold climates / Earth system models / eco‐evolutionary optimality theory / Enzyme kinetics / Enzymes / Gas exchange / Global warming / Kinetics / Photosynthesis / Respiration / Temperature / Temperature rise / thermal acclimation / Vapor pressure / Vapour pressure / Warm climates