Prolonged warming and drought reduce canopy-level net carbon uptake in beech and oak saplings despite photosynthetic and respiratory acclimation

Tree net carbon (C) uptake may decrease under global warming, as higher temperatures constrain photosynthesis while simultaneously increasing respiration. Thermal acclimation might mitigate this negative effect, but its capacity to do so under concurrent soil drought remains uncertain. Using a five-year open-top chamber experiment, we determined acclimation of leaf-level photosynthesis (thermal optimum Topt and rate Aopt) and respiration (rate at 25°C R25 and thermal sensitivity Q10) to chronic +5°C warming, soil drought, and their combination in beech (Fagus sylvatica L.) and oak (Quercus pubescens Willd.) saplings. Process-based modeling was used to evaluate acclimation impacts on canopy-level net C uptake (Atot). Prolonged warming increased Topt by 3.03-2.66°C, but only by 1.58-0.31°C when combined with soil drought, and slightly reduced R25 and Q10. In contrast, drought reduced Topt (-1.93°C in oak), Aopt (~50%), and slightly reduced R25 and Q10 (in beech). Mainly because ..., , # Prolonged warming and drought reduce canopy-level net carbon uptake in beech and oak saplings despite photosynthetic and respiratory acclimation

## Physiological measurements

* **Filename: \"Deluigi 2025 - Water potentials and environmental conditions.csv\"**

Leaf water potentials at predawn and midday and air temperature and soil moisture conditions measured for each sapling of each species during three campaigns (June, August, September) in 2022 and 2023 in all climatic treatments

-Chamber: code for individual open-top chamber (see Fig. S2 for the experimental design in the Supplementary information)
-Treatment: code for climatic treatment: C = control, D = drought, H = warming, HD = hot drought
-Campaign: measurement campaign (June, August or September) for the two years of measurement (2022, 2023)
-Heating: YES/NO variable for climatic treatments with increased air temperature (+5°C compared to the control)
-Drought: YES/NO variable for climatic treatments with reduced soil mois...,