DOI: 10.5061/dryad.bzkh189kg
title: Epidermal cell length of <em>Bursera</em> <em>simaruba</em> and <em>Eucalyptus camaldulensis</em> leaves

description: Tree height varies across environments, with taller individuals found in
 cool, moist habitats and shorter trees in drier regions. Within species,
 trees can exhibit height variation due to environmental factors such as
 drought-induced dieback. A key question is what drives changes in leaf
 structure with increasing height–whether some trait values cannot be
 produced under the developmental conditions at treetops or whether
 differences arise because natural selection favors particular trait values
 at different canopy positions. Some hypotheses suggest that increasing
 height imposes limits on mature leaf traits, making some structural
 changes developmentally inevitable. However, selection could also favor
 structural changes within wide fields of developmentally possible trait
 configurations. We examined leaf epidermal cell size distributions in
 Bursera simaruba and Eucalyptus camaldulensis from seedlings to maximum
 tree heights in situations in which seedlings to adults were all exposed
 to full sun and thus had all “sun” leaves. We found that in general, cell
 sizes increased, variance remained high, and distributions did not
 systematically shift with height. These results indicate that, rather than
 reflecting a developmental inability to produce certain leaf epidermal
 cell sizes at greater heights, the patterns we observed are better
 explained by selection simply favoring some cell sizes from among the many
 that development can produce.
description: The turgor limitation hypothesis suggests that if a tree is
 approaching or has reached its height limit under given environmental
 conditions, its leaf cells should display signs of restricted expansion
 due to reduced turgor at greater heights. This hypothesis implies that
 these conditions "limit" the tree from producing the cell sizes
 that natural selection would otherwise favor. As a result, natural
 selection should favor individuals capable of producing cell sizes as
 close as possible to the optimal values. The turgor limitation hypothesis
 thus predicts a distinct cell size frequency distribution, characterized
 by strong negative skewness and low variance. We used
 two sampling strategies to test the predictions of the turgor limitation
 hypothesis. 1- Seedlings to maximum tree size within a
 species: We analyzed the distribution of leaf epidermal cell dimensions in
 different individuals of the same species, from seedlings to the tallest
 individuals at our study site. We selected a species that is uniformly
 exposed to the sun across all size classes. On the coastal plain near the
 Los Tuxtlas field station, Veracruz, Mexico, <em>Bursera
 simaruba</em> (L.) Sarg. (Burseraceae, Sapindales) is used as a
 living fence in cattle pastures. This means that the terrain is maximally
 open and sunny, with even small individuals exposed to full sun. We
 collected the apicalmost leaves from 29 individuals ranging in height from
 14.5 cm to 26.6 m. 2- Trees experiencing dieback: We
 also study the distribution of leaf cell lengths of trees of the same
 species, with different heights, where the taller individuals experienced
 dieback. Our second strategy involved sampling a population of
 <em>Eucalyptus camaldulensis</em> Dehnh. (Myrtaceae, Myrtales)
 experiencing dieback in University City, of the National Autonomous
 University of Mexico (UNAM). As we did with <em>Bursera
 simaruba</em>, we collected the uppermost leaves of 29 individuals
 of <em>Eucalyptus</em> camaldulensis*, with heights ranging
 from 1.09 m to 23 m. All of the large individuals showed evidence of
 dieback. We collected the uppermost leaves from each
 tree across all three sampling strategies. For trees under 8 meters tall,
 we used clippers or pruner poles, while for taller trees, we employed a
 DeLeaves canopy sampling system (Outreach Robotics, Quebec, Canada)
 mounted on a Matrice 300 RTK drone (DJI, Shenzhen, China). Tree heights
 were measured with a tape measure, and for the tallest trees, we utilized
 a Mini 4 Pro drone (DJI, Shenzhen, China) equipped with an onboard
 barometric altimeter. Anatomical methods and
 measurement of quantitative variables:  We preserved
 the leaves in 70% ethanol and then created stomatal impressions using the
 nail polish method. These impressions were mounted on slides, observed
 under a compound microscope, and photographed with a digital camera. From
 the stomatal impressions, we measured the lengths of guard subsidiary and
 pavement cells, 100 cells each, using ImageJ 1.53k, with images calibrated
 using a Nikon stage micrometer (MBM13100, Nikon Corp., Tokyo, Japan) to
 convert cell length measurements from pixels to micrometers.
description: # Epidermal cell length of *Bursera* *simaruba* and *Eucalyptus
 camaldulensis* leaves
 [https://doi.org/10.5061/dryad.bzkh189kg](https://doi.org/10.5061/dryad.bzkh189kg) ## Description of the data and file structure ### Files and variables #### File: Turgor_limitation_Leaf_cell_lengths.xlsx **Description:** The file titled "Turgor limitation_Leaf cell lengths" includes all recorded data on cell lengths and tree heights for *Bursera simaruba* and *Eucalyptus camaldulensis* with different heights. The data is organized into the following columns: ##### Variables * **Group**: Identifier for sampling strategy (*simaruba, eucalyptus*). * **Order**: Orders according to the website Plants of the World Online (POWO, 2024). * **Family**: Families according to the website Plants of the World Online (POWO, 2024). * **Genus**: Genera according to the website Plants of the World Online (POWO, 2024). * **Species**: Species names according to the website Plants of the World Online (POWO, 2024). * **Authority**: Authorities for the scientific names according to the website Plants of the World Online (POWO, 2024). * **Individual**: Numbering of all sampled individuals: *Bursera simaruba* (1-29), and *Eucalyptus camaldulensis* (30-58). * **Height (m)**: Height of *Bursera simaruba* and *Eucalyptus camaldulensis* individuals. * **µm, length Guard Cells**: Length of guard cells in µm. * **Log10, length Guard Cells**: Guard cell length in µm, transformed into Log10. * **µm, length Subsidiary Cells**: Length of subsidiary cells in µm. * **Log10, length Subsidiary Cells**: Subsidiary cell length in µm, transformed into Log10. * **µm, length Pavement Cells**: Length of pavement cells in µm. * **Log10, length Pavement Cells**: Pavement cell length in µm, transformed into Log10. ## Code/software To view the data, Microsoft Excel or similar software is required.