DOI: 10.5061/dryad.fxpnvx14f
title: Prolonged warming and drought reduce canopy-level net carbon uptake in beech and oak saplings despite photosynthetic and respiratory acclimation

description: 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 of reduced leaf area, Atot decreased by 47-84% with
 warming (in beech) and drought, but without additive effects when
 combined.  Our results suggest that, despite photosynthetic and
 respiratory acclimation to warming and soil drought, canopy-level net C
 uptake will decline in a persistently hotter and drier climate, primarily
 due to the prevalent impact of leaf area reduction.
description: # 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
 moisture (-50% soil water content compared to the control) -Mixture:
 mixture combination: Single = one individual of one species (n = 1),
 Monoculture = four individuals of one species (n = 4), Mixture = two
 individuals for each species (n = 4) -Species: code for each tree species:
 B = beech, O = oak -Tree: label number of each individual measured sapling
 for each species in all climatic treatments -WP_predawn: leaf water
 potential at predawn (MPa) -WP_midday: leaf water potential at midday
 (MPa) -Tair_lag: Air temperature (°C) of the day before measuring the leaf
 water potentials at predawn and midday for the measured sapling growing in
 the respective open-top chamber -SWC_lag: Soil water content (%) of the
 day before measuring the leaf water potentials at predawn and midday for
 the measured sapling growing in the respective open-top chamber
 -Tair_mean: Air temperature (°C) of the same day of measurement of the
 leaf water potential at predawn for the measured sapling growing in the
 respective open-top chamber -SWC_mean: Soil water content (%) of the same
 day before measuring of the leaf water potential at midday for the
 measured sapling growing in the respective open-top chamber * **Filename:
 "Deluigi 2025 - Aopt Topt R25 Q10 water potentials and environmental
 conditions.csv"** Temperature response curves parameters extracted
 from temperature response curves of photosynthesis and respiration
 measured for each sapling of each species during three campaigns (June,
 August, September) in 2022 and 2023 in all climatic treatments, with
 respective air temperature and soil moisture conditions of the day of
 measurements or previous days (1,3,15 and 30 days of interval). -Campaign:
 measurement campaign (June, August or September) for the two years of
 measurement (2022, 2023) -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 -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
 moisture (-50% soil water content compared to the control) -Mixture:
 mixture combination: Single = one individual of one species (n = 1),
 Monoculture = four individuals of one species (n = 4), Mixture = two
 individuals for each species (n = 4) -Tree: label number of each
 individual measured sapling for each species in all climatic treatments
 -WP_predawn: leaf water potential at predawn (MPa) -WP_midday: leaf water
 potential at midday (MPa) -Tair_2m_mean: average daytime air temperature
 (°C) measured at 2m height inside each individual chamber during the day
 of measurement of the temperature response curves of photosynthesis and
 respiration for each measured sapling growing in the respective open-top
 chamber -Tair_1d_mean: average daytime air temperature (°C) measured at 2m
 height inside each individual chamber the day before the day of
 measurement of the temperature response curves of photosynthesis and
 respiration for each measured sapling growing in the respective open-top
 chamber -Tair_3d_mean: average daytime air temperature (°C) measured at 2m
 height inside each individual chamber three days before the day of
 measurement of the temperature response curves of photosynthesis and
 respiration for each measured sapling growing in the respective open-top
 chamber -Tair_15d_mean: average daytime air temperature (°C) measured at
 2m height inside each individual chamber fifteen days before the day of
 measurement of the temperature response curves of photosynthesis and
 respiration for each measured sapling growing in the respective open-top
 chamber -Tair_30d_mean: average daytime air temperature (°C) measured at
 2m height inside each individual chamber thirty days before the day of
 measurement of the temperature response curves of photosynthesis and
 respiration for each measured sapling growing in the respective open-top
 chamber -SWC_2m_mean: average daytime soil water content (%) measured
 inside each individual chamber during the day of measurement of the
 temperature response curves of photosynthesis and respiration for each
 measured sapling growing in the respective open-top chamber -SWC_1d_mean:
 average daytime soil water content (%) measured inside each individual
 chamber the day before the day of measurement of the temperature response
 curves of photosynthesis and respiration for each measured sapling growing
 in the respective open-top chamber -SWC_3d_mean: average daytime soil
 water content (%) measured inside each individual chamber three days
 before the day of measurement of the temperature response curves of
 photosynthesis and respiration for each measured sapling growing in the
 respective open-top chamber -SWC_15d_mean: average daytime soil water
 content (%) measured inside each individual chamber fifteen days before
 the day of measurement of the temperature response curves of
 photosynthesis and respiration for each measured sapling growing in the
 respective open-top chamber -SWC_30d_mean: average daytime soil water
 content (%) measured inside each individual chamber thirty days before the
 day of measurement of the temperature response curves of photosynthesis
 and respiration for each measured sapling growing in the respective
 open-top chamber -Aopt: photosynthetic rate at the thermal optimum of
 photosynthesis (µmol m-2 s-1) -Topt: thermal optimum of photosynthesis
 (°C) -R25: respiration rate measured at a standard temperature of 25°C
 (µmol m-2 s-1) -Q10: thermal sensitivity of respiration * **Filename:
 "Deluigi 2025 - Total leaf area and tree size.csv"** Plant total
 leaf area and sapling size measured for all saplings of each species in
 all climatic treatments in 2022-2023 -Year: year of measurement -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
 -Species: code for each tree species: B = beech, O = oak -Mixture: mixture
 combination: Single = one individual of one species (n = 1), Monoculture =
 four individuals of one species (n = 4), Mixture = two individuals for
 each species (n = 4) -Tree: label number of each individual measured
 sapling for each species in all climatic treatments -numb_leaf: number of
 leaf counted for each sapling -leaf_size: average leaf size (cm2)
 estimated from 10 individual pictures taken at different heights of the
 sapling -WT_LA: plant total leaf area (m2) estimated by multiplying the
 number of leaves by the average leaf size -height: sapling height (cm)
 -DBH: sapling diameter (mm), measured at 20 cm from the ground ## SPAC
 model simulation * **Filename: "Deluigi 2025 - SPAC\_ environmental
 conditions.RDS"** Environmental conditions measured inside each
 individual open-top chamber in 2022-2023 used for the SPAC simulation
 -Chamber: code for individual open-top chamber (see Fig. S2 for the
 experimental design in the Supplementary information) -TIMESTAMP: date and
 time of measurement (format: YYY-MM-DD HH:MM:SS) -Ta: air temperature (°C)
 measured at 2m height -RH: relative humidity (%) measured at 2m height
 -VPD: vapor pressure deficit (kPa) calculated from air temperature and
 relative humidity measurements -Pa: atmospheric pressure (kPa) -PPFD:
 photosynthetic photon flux density (µmol m-2 s-1) -SWR: short wave
 radiation (W m-2) -Psi_soil: soil water potential (calculated from soil
 water content) (kPa) -WS: wind speed (m s-1) -Ca: atmospheric CO2
 concentration (ppm) * **Filename: "Deluigi 2025 - SPAC_plant
 traits.csv"** Plant traits used for the SPAC simulation
 -Acclimation_type: type of acclimation included in the SPAC model: all =
 all traits (i.e., average values of ToptVcmax , ToptJmax, R25, Q10, and
 LAI for each species, climatic treatment, and year), only_LA = only
 acclimation of total leaf area, but not photosynthesis and respiration,
 only_AR = only acclimation of photosynthesis and respiration, but not
 total leaf area -Year: year of measurement -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 -Species: code for
 each tree species: B = beech, O = oak -vcmax: carboxylation capacity at
 25°C (µmol m-2 s-1) -jmax: electron transport capacity at 25°C (µmol m-2
 s-1) -vcmax_Topt: thermal optimum (°C) of vcmax -jmax_Topt: thermal
 optimum (°C) of jmax -vcmax_Tmax: maximal temperature (°C) of vcmax
 -jmax_Tmax: maximal temperature (°C) of jmax -R25:respiration rate
 measured at a standard temperature of 25°C (µmol m-2 s-1) -Q10: thermal
 sensitivity of respiration -LAI: leaf area index (m2 m-2) calculated from
 the measured total leaf area (m2) divided by the compartment area (6 m2)
 -g0: minumun leaf stomatal conductance (mmol m-2 s-1) -s_f: stomatal
 sensitivity to leaf water potential -m: proportionality factor between
 stomatal conductance and photosynthesis -Psi_f: leaf water potential for
 stomatal closure (point of stomatal closure) (kPa) -flush_date: date of
 leaf flush in spring -fall_date: date of leaf senescence in autumn *
 **Filename: "Deluigi 2025 - SPAC simulated daily canopy-level A and
 R.csv"** SPAC output of daily simulated photosynthetic and
 respiration rates for each species in all climatic treatments in 2022 and
 2023 -Species: code for each tree species: B = beech, O = oak -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 -Date:
 date, format M/D/YYYY -Month: month of the year, format YY-Mon (Mon =
 month abbreviation: Jan, Feb, ...) -Year: year of measurement -A_day:
 avreage simulated net photosynthetic rate (µmol m-2 s-1), averaged for
 each date -A_day_se: standard error of the averaged net photosynthetic
 rate -R_day: avreage simulated respiration rate (µmol m-2 s-1), averaged
 for each date -R_day_se: standard error of the averaged respiration rate
 -Agross_day: avreage simulated gross photosynthetic rate (µmol m-2 s-1),
 averaged for each date -Agross_day_se: standard error of the averaged
 gross photosynthetic rate -Tair: air temperature (°C) measured at 2m
 height -VPD: vapor pressure deficit (kPa) calculated from air temperature
 and relative humidity -PPFD: photosynthetic photon flux density (µmol m-2
 s-1) -Psi_soil: soil water potential (kPa) calculated from soil water
 content -acclimation: type of acclimation included in the SPAC model: all
 = all traits (i.e., average values of ToptVcmax , ToptJmax, R25, Q10, and
 LAI for each species, climatic treatment, and year), only_LA = only
 acclimation of total leaf area, but not photosynthesis and respiration,
 only_AR = only acclimation of photosynthesis and respiration, but not
 total leaf area * **Filename: "Deluigi 2025 - SPAC simulated Atot
 Agross tot and Rtot.csv"** Yearly sum of the hourly modeled
 canopy-level net photosynthesis, gross photosynthesis and respiration for
 each acclimation level, climatic treatment, and species over two years of
 measurement -Species: code for each tree species: B = beech, O = oak
 -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 -Year: year of measurement -Atot: Yearly sum of the hourly modeled
 canopy-level net photosynthesis (gCO2) -Rtot: Yearly sum of the hourly
 modeled canopy-level respiration rate (gCO2) -Agrosstot: Yearly sum of the
 hourly modeled canopy-level gross photosynthesis (gCO2) -acclimation: type
 of acclimation included in the SPAC model: all = all traits (i.e., average
 values of ToptVcmax , ToptJmax, R25, Q10, and LAI for each species,
 climatic treatment, and year), only_LA = only acclimation of total leaf
 area, but not photosynthesis and respiration, only_AR = only acclimation
 of photosynthesis and respiration, but not total leaf area -Drought:
 YES/NO variable for climatic treatments with reduced soil moisture (-50%
 soil water content compared to the control) -Heating: YES/NO variable for
 climatic treatments with increased air temperature (+5°C compared to the
 control) delta_C: difference between the Atot of each climatic treatment
 (D, H and HD) and the control (C)