DOI: 10.5061/dryad.7pvmcvf23
title: Data from: Contrasting heat tolerance of evergreen and deciduous urban woody species during heat waves

description: The increasing frequency and intensity of heat waves caused significant
 damages to urban woody species, and the different leaf structures between
 evergreen and deciduous species may be closely related to leaf heat
 tolerance. However, whether the different leaf structural traits of
 evergreen and deciduous plants contribute to their different responses
 under heat waves is still unclear. During the record-breaking and
 long-lasting 2022 summer heat waves in China, we investigated the
 relationships between leaf thermal indices and leaf structural traits of
 36 urban woody species in four cities along the Yangtze River. We found
 that all the four thermal indices were significantly but weakly related
 with leaf damage status. The critical temperature that causes the initial
 15% damage to photosystem II (Tcrit) may serve as a sensitive measure of
 heat tolerance. Evergreen species suffered less leaf damage during the
 heat waves and exhibited higher leaf heat tolerance, thicker leaves than
 deciduous species. Tcrit was significantly correlated with leaf mass per
 area, leaf thickness and thickness of spongy tissue. Synthesis: Urban
 woody species with high Tcrit, leaf mass per area, and leaf thickness tend
 to be more tolerant to heat stress. This study provides insights for
 predicting leaf heat tolerance of urban woody plants in subtropical China
 and their physiological and ecological responses to severe heat waves.
description: <strong>Quantify leaf damage status (LDR,
 Fv/Fm)</strong><strong>：</strong> (1)
 Leaf damage ratio (LDR). To quantify physical leaf tissue damage caused by
 heat waves, we visually assessed and recorded the percentage of damaged
 leaves in the entire plant canopy as LDR following Esperon-Rodriguez et
 al. (2021). Specifically, burned areas on the leaf surface associated with
 a color change from green to light brown with dark brown margins were
 considered as leaf damage. Two fixed people scored the LDR of each tree,
 and if their results were similar (within 10% difference), the average
 value was taken. If the results differed greatly, a third evaluator was
 asked to provide more information to achieve a more accurate value. We
 evaluated five replicates per species, and the final average was taken to
 represent the LDR. (2) The maximum quantum efficiency
 (Fv/Fm) of the leaf photosystem II. We sampled 3-5 individuals per
 species, collected over twenty leaves for each individual (totally 60-100
 leaves per species), and brought them to the laboratory. After a 2h 25℃
 dark treatment of the leaf samples, we measured Fv/Fm of the leaf
 photosystem II with PAM 2500 fluorometer (Walz, Effeltrich,
 Germany). <strong>Measure leaf photosynthetic
 heat tolerance (Tcrit, T50, TSM):</strong> We set
 up nine water baths to measure leaf heat tolerance, the control bath was
 set at 26°C and the experimental water baths were set at 36, 41, 46, 50,
 52, 54, 56 and 60°C, respectively. Leaf samples were kept in the dark for
 at least two hours in plastic bags with moist paper tissues. For each
 species, leaves were cut into many 4 cm<sup>2</sup> pieces and
 6-8 pieces were placed into a sealed plastic bag (nine plastic bags for
 nine temperature gradients) in water bath for 15 minutes, followed by 24
 hours of dark adaptation. Fv/Fm was recorded to detect leaf irreversible
 damage caused by temperature treatments. Tcrit and T50 of each species
 were derived using a Weibull function fitted to Fv/Fm versus treatment
 temperature using the R package <em>fitplc</em> (Drake et al.,
 2018), showing the critical temperature (Tcrit) that causes the initial
 damage (15%) and the temperature (T50) that causes 50% damage to
 photosystem II. To determine the thermal safety margin
 (TSM), we measured the maximum leaf temperature (Tleafmax) of each species
 (3-5 individuals) during 12:00-14:00 (Marchin et al., 2022) in the same
 day in each city with an infrared thermal camera (FLIR, America). We tried
 our best to ensure that leaf temperatures of fully sun-exposed leaves are
 comparable across species in each city within a short period, as reported
 in previous studies (Blasini et al., 2022; Lin et al., 2017). Moreover,
 the maximum leaf temperature recorded for each species in each city on a
 given day can be measured accurately to calculate TSM. TSM is the
 difference between T50 or Tcrit and Tleafmax (i.e., TSMcrit = Tcrit -
 Tleafmax), following the method described by Kitudom (2022). This metric
 provides a good prediction of leaf heat vulnerability, with the threshold
 of leaf temperature reached when Tleafmax equals Tcrit or T50.
 <strong>Measure leaf morphological traits (LA,
 LMA):</strong> For each species (3-5 replicates),
 twenty leaves from each replicate were scanned using a flatbed scanner (HP
 Deskjet 1050). Leaf area (LA, cm<sup>2</sup>) was analyzed
 using ImageJ (National Institutes of Health, Bethesda, USA) based on the
 scanned image. Then leaves were dried (65 °C for 72h) and their masses
 were determined. Leaf mass per area (LMA, g/cm<sup>2</sup>)
 was calculated by the ratio of leaf dry weight to leaf area.
 <strong>Measure leaf anatomical traits (LT, Tup, Tlow, Tp,
 Ts, P/S, GCL, SD, SPI)</strong> We made cross
 sections of leaves using the freehand sectioning method. We measured leaf
 thickness (LT, µm) and thickness of upper and lower epidermis (Tup, Tlow),
 palisade mesophyll (Tp), and spongy mesophyll (Ts). All cross sections
 were photographed with a microscope (YS100, Nikon, Tokyo, Japan) at 40×
 magnification, and analyzed by Image J software. Three images were
 captured from each of four leaves per species. To
 measure the stomatal traits, epidermal peels from both leaf surfaces of
 four leaves per species were used to determine stomatal traits (guard cell
 length (GCL), stomatal pore length (SL) and stomatal density (SD). We used
 a layer of transparent nail polish to fix the stomata of the leaves. The
 nail polish layer was then glued to a piece of transparent tape cut into
 1.0 cm × 1.0 cm and flattened on a microscope slide before being covered
 with a coverslip for imaging. All images were captured using a microscope
 (YS100, Nikon, Tokyo, Japan), and analyzed using Image J software. Three
 images of epidermal peels were captured from each of four leaves per
 species. At 400× magnification, we scored guard cell length (GCL, µm) and
 stomatal pore length (SL, µm). At 100× magnification, we counted stomata
 in a 0.25 mm<sup>2</sup> field of view to determine stomatal
 density (SD, mm<sup>-2</sup>), calculating stomatal pore index
 (SPI = SD×SL<sup>2</sup>).
 <strong>Reference:</strong>
 Blasini, D. E., Koepke, D. F., Bush, S. E., Allan, G. J.,
 Gehring, C. A., Whitham, T. G., Day, T. A., & Hultine, K. R.
 (2022). Tradeoffs between leaf cooling and hydraulic safety in a dominant
 arid land riparian tree species. <em>Plant Cell and
 Environment</em>, <em>45</em>(6), 1664–1681.
 https://doi.org/10.1111/pce.14292 Drake, J. E.,
 Tjoelker, M. G., Vårhammar, A., Medlyn, B. E., Reich, P. B., Leigh, A.,
 Pfautsch, S., Blackman, C. J., López, R., Aspinwall, M. J., Crous, K. Y.,
 Duursma, R. A., Kumarathunge, D., De Kauwe, M. G., Jiang, M., Nicotra, A.
 B., Tissue, D. T., Choat, B., Atkin, O. K., & Barton, C. V. M.
 (2018). Trees tolerate an extreme heatwave via sustained transpirational
 cooling and increased leaf thermal tolerance. <em>Global Change
 Biology</em>, <em>24</em>(6), 2390–2402.
 https://doi.org/10.1111/gcb.14037 Esperon-Rodriguez,
 M., Power, S. A., Tjoelker, M. G., Marchin, R. M., & Rymer, P. D.
 (2021). Contrasting heat tolerance of urban trees to extreme temperatures
 during heatwaves. <em>Urban Forestry & Urban
 Greening</em>, <em>66</em>, 127387.
 https://doi.org/10.1016/j.ufug.2021.127387 Kitudom, N.,
 Fauset, S., Zhou, Y., Fan, Z., Li, M., He, M., Zhang, S., Xu, K.,
 & Lin, H. (2022). Thermal safety margins of plant leaves across
 biomes under a heatwave. <em>Science of The Total
 Environment</em>, <em>806</em>, 150416.
 https://doi.org/10.1016/j.scitotenv.2021.150416 Lin,
 H., Chen, Y., Zhang, H., Fu, P., & Fan, Z. (2017). Stronger
 cooling effects of transpiration and leaf physical traits of plants from a
 hot dry habitat than from a hot wet habitat. <em>Functional
 Ecology</em>, <em>31</em>(12), 2202–2211.
 https://doi.org/10.1111/1365-2435.12923 Marchin, R. M.,
 Backes, D., Ossola, A., Leishman, M. R., Tjoelker, M. G., &
 Ellsworth, D. S. (2022). Extreme heat increases stomatal conductance and
 drought-induced mortality risk in vulnerable plant species.
 <em>Global Change Biology</em>, <em>28</em>(3),
 1133–1146. https://doi.org/10.1111/gcb.15976
description: # Contrasting heat tolerance of evergreen and deciduous urban woody
 species during heat waves
 [https://doi.org/10.5061/dryad.7pvmcvf23](https://doi.org/10.5061/dryad.7pvmcvf23) We have submitted our raw data (Data.xls). There are two sheets in the “Data” table. **MetaData** lists the paper title, abbreviation of all the names of each column in the RawData **RawData** is the raw data; any missing values are shown as "NA" to minimize ambiguity. ## Description of the data and file structure ### Data: * Species: Scientific name of the species * City: Study sites * Leafhabit: evergreen and deciduous * EHF: Excess heat factor * LDR: Leaf damage ratio (%) * Fv/Fm: The maximum quantum efficiency of the leaf photosystem II (unitless) * Tleafmax: The maximum temperature of leaf during the day (°C) * Tcrit : The critical temperature causes the initial damage (15%) to Fv/Fm (°C) * T50: The temperature causes 50% damage to Fv/Fm (°C) * TSMcrit: The difference between thermal tolerance (Tcrit) and Tleafmax (°C) * TSM50: The difference between thermal tolerance (T50) and Tleafmax (°C) * LMA: Leaf mass per area (g/m2) * LA: Individual leaf area (cm2) * LT: Leaf thickness (μm) * Tup: Thickness of upper epidermis (μm) * Tlow: Thickness of lower epidermis (μm) * Tp: Thickness of palisade tissue (μm) * Ts: Thickness of spongy tissue (μm) * P/S: The ratio of thickness of palisade tissue to spongy tissue (unitless) * GCL: Guard cell length (μm) * SD: Stomatal density (mm-2) * SPI: Stomatal pore index (unitless)