DOI: 10.5061/dryad.9zw3r22rp
title: Quantifying uncertainties in leaf thermal thresholds and their implications for photosynthetic recovery

description: Understanding plant heat tolerance requires assessing their thermal
 thresholds, but commonly used methods have rarely been compared. Moreover,
 whether the photosynthetic machinery is irreversibly damaged past these
 thresholds remains unclear. We determined the critical
 temperature (Tcrit), the temperature causing a 50% reduction (T50), and
 the maximum tolerable temperature (Tmax) of photosystem II in
 Mediterranean cypress, Aleppo pine, and Scots pine saplings using 15- or
 30-min heat exposure curves performed on living plants (in-vivo), excised
 needles (ex-vivo), and excised needles continuously exposed to each rising
 temperature (ex-vivo continuous). Dark-adapted fluorescence (Fv/Fm) and
 gas exchange were recorded for four days post-heat stress to track
 recovery. Longer heat exposure (30 vs. 15min)
 consistently led to lower Fv/Fm, T50, and Tmax. T50 and Tmax were reduced
 in both ex-vivo conditions compared to in-vivo ones. Conversely, Tcrit
 remained consistent between species, exposure durations, and methods. Gas
 exchange and Fv/Fm recovery mainly occurred before reaching T50 values
 (about 45°C). Our work highlights the importance of exposure
 duration and method selection when measuring and comparing thermal
 thresholds. Moreover, while Tcrit appears to be a reversible threshold,
 the photosynthetic machinery of studied species appears irreparably
 damaged past their T50.
description: # Quantifying uncertainties in leaf thermal thresholds and their
 implications for photosynthetic recovery
 [https://doi.org/10.5061/dryad.9zw3r22rp](https://doi.org/10.5061/dryad.9zw3r22rp) ## Description of the data and file structure In November 2023, eight branches per tree were selected and marked over the entire canopy (n = 144 branches in total; 6 trees x 3 species x 8 branches). Among the six repetitions per species, three trees were used for the 15 min exposure time and three for the 30 min one (see below). Physiological traits related to thermal thresholds were all measured at the same location, with similar light and temperatures conditions, on the selected branches. Between the measurements, which lasted two months, all plants remained in the greenhouse. ### Files and variables #### File: Dryard\_Data\_PCE\_MargauxDidionGency.xlsx **Description:** Metadata for tab "Dryard Data_PCE_MargauxDidionGency" | Column | Entry | Value | Unit | Explanation | Remark | | :----- | :-------- | :-------- | :--- | :-------------------------------------------------------------------------------------------------- | :----- | | A | ID name | 18 | | Tree number | | | B | Method | 3 | | Method (in-vivo, ex-vivo, ex-vivo continuous) | | | C | Location | 1 | | Storage place between measurement | | | D | Species  | 3 | | Species (Pinus sylvestris, Pinus halepensis, Cupressus sempervirens)  | | | E | Exposure | 2 | min | Exposure duration (15 or 30min) | | | F | Replicate | 3 | | Replicate for each species, exposure duration and method | | | G | Tcrit | Numerical |   | Critical leaf temperature that induces an abrupt decrease in the photosynthetic efficiency of PSII  |   | | H | Tmax | Numerical | | Maximum tolerable temperature of PSII  | | | I | T50 | Numerical | | Temperature causing a 50% reduction in the maximum quantum yield of PSII | | #### File: Dryard\_Data2\_PCE\_MargauxDidion-Gency.xlsx **Description:** Metadata for tab "Dryard Data2_PCE_MargauxDidionGency" | Column | Entry | Value | Unit | Explaination | Remark | | :----- | :---------- | :-------- | :-------- | :-------------------------------------------------------------------- | :----- | | A | Day | 4 | | Day (0, 1, 2, 3, 4) | | | B | ID name | 18 | | Tree number | | | C | Method | 3 | | in-vivo | | | D | Location | 1 | | Storage place between measurement | | | E | Species  | 3 | | Species (Pinus sylvestris, Pinus halepensis, Cupressus sempervirens)  | | | F | Exposure | 2 | min | Exposure duration (15 or 30min) | | | G | Replicate | 3 | | Replicate for each species, exposure duration and method | | | H | Branch | 7 | | Seven branch per tree were measured | | | I | Temperature | 7 | °C | Seven temperature per tree were measured |   | | J | FvFm | Numerical | - | maximum photochemical efficiency  | | | K | FvFm\_p | Numerical | % | percentage of maximum photochemical efficiency  | | | L | Asat | Numerical | µmol/m²/s | light-saturated assimilation  | | | M | Asat\_p | Numerical | % | percentage of light-saturated assimilation  | | | N | Gs | Numerical | mol/m²/s | stomatal conductance  | | | O | Gs\_p | Numerical | % | percentage of stomatal conductance  |   | NA=not available