DOI: 10.5061/dryad.0cfxpnwbx
title: Physiological and morphological growth and hydraulic measures in Asclepias syriaca and A. speciosa under drought

description: Understanding factors that determine a species’ geographical range is
 crucial for predicting climate-induced range shifts. Two milkweed species,
 Asclepias syriaca and Asclepias speciosa, have overlapping ranges along a
 moisture gradient in North America and are primary food sources for
 endangered monarch caterpillars. With decreasing moisture, long-lived
 species often exhibit slower growth and greater drought tolerance while
 many annual species exhibit faster growth strategies. Using this fast-slow
 framework, we assessed whether traits of these two sister species differ
 along a fast-slow growth continuum and could explain their distributions.
 We measured leaf and root functional traits in common gardens and
 greenhouse experiments. In key measures indicative of drought tolerance
 (e.g., growth, transpiration, and water potentials) the species were
 nearly identical. Contrary to expectations, A. speciosa did not exhibit
 greater drought tolerance, raising the question of how it survives in the
 more arid west. A reciprocal transplant study showed selection against A.
 syriaca in the western garden and that A. speciosa was better able to
 avoid seedling mortality. Focusing on seedling establishment, we found
 that A. speciosa exhibited faster deep root development and a narrow leaf
 phenotype associated with slower wilting and delayed drought-induced
 mortality. Rather than differences on the fast slow growth spectrum, our
 results indicate that A. speciosa avoids drought through faster deep root
 growth and a slower wilting phenotype. Our study suggests that A.
 syriaca’s range is limited by its drought tolerance, while A. speciosa
 employs a number of drought avoidance strategies to survive in more arid
 environments. 
description: The data sets are a combination of greenhouse experiments and
 field studies.  
description: # Asclepias syriaca and speciosa drought tolerance
 [https://doi.org/10.5061/dryad.0cfxpnwbx](https://doi.org/10.5061/dryad.0cfxpnwbx) ## Description of the data and file structure ### Files and variables #### File: 2019\_Milkweed\_Leaf\_width\_data.xlsx **Description:** Contains plant height and leaf width information for genotypes of *A. speciosa* and *A. syriaca* collected from South Dakota and Minnesota.  Latitude and longitude of collection sites are given.  Leaf width was measured on different leaves for each plant 3x and averaged.  Cells with N/A for plant height or leaf width measures indicate a plant that did not germinate or plants that only had one or two leaves for measurement.  ##### Variables: * Plant height (cm) * Leaf width 1 (mm) * Leaf width 2 (mm) * Leaf width 3 (mm) * Leaf width Average (mm) #### File: Milkweed\_LiCor\_Data.xlsx **Description:** Gas exchange data using a LiCor 6400 system are given for genotypes of *A. speciosa* and *A. syriaca* measured in September of 2020 or March of 2021.  Latitude and longitude of where the milkweed were collected are also given.  The missing values dark respiration values for March are due to the student forgetting to take the dark respiration measures.    ##### Variables * Amax  or maximum assimilation rate (µmol m⁻² s⁻¹) * Dark Respiration (µmol m⁻² s⁻¹) * Quantum Yield (μmol m⁻² s¹ CO2 / μmol m⁻² s-¹ light * A/gs or Assimilation/stomatal conductance (µmol mol⁻¹) * Ci or Internal CO2 (ppm) * gs or Stomatal Conductance (mol m⁻² s-¹) * E or Transpiration (mol m⁻² s-¹) * A/E or Assimilation/transpiration (μmol mol⁻¹) #### File: Milkweed\_Stomatal\_gs\_density\_and\_length.xlsx **Description:** Contains stomatal density and length information for genotypes of *A. speciosa* and *A. syriaca* collected from South Dakota and Minnesota.  Latitude and longitude of collection sites are given.  ##### Variables * Stomatal Length (mm) * Stomatal Density (# Stomata/mm2) #### File: Wilting\_and\_root\_Combined\_data\_set.xlsx **Description:** Contains information on the time for roots to reach the bottom of 22 cm pot and # days until wilting for genotypes of *A. speciosa* and *A. syriaca* collected from across the United States.  Latitude and longitude of collection sites are given.  The missing value for # of days for roots to reach bottom was for one plant whose roots never did reach the bottom.  The missing values for biomass was for the last batch of plants which were accidentally thrown away before their weights were recorded.   ##### Variables * Plant Height (cm) * Leaf width (mm) * The # Leaves * Total Plant Biomass (g) * The # of days since stopped watering until plants wilted * The # of days for roots to reach bottom of 22 cm tall pots #### File: 2019\_Milkweed\_GH\_Drought.xlsx **Description:** Contains information on the variables measured for a greenhouse drought experiment for genotypes of *A. speciosa* and *A. syriaca* collected from South Dakota.  Latitude and longitude of collection sites are given.  There were four water treatments (High, Medium High, Medium Low, and Low) and the plants were randomized within four blocks.  The missing values within the data set (N/A) are mostly the result of only a subset of the plants be measured for a particular variable (for example leaf area, vessel area, vessel density, water potential etc.).   ##### Variables * Biomass (g) * Leaf weight (g) * Leaf area (sm2) * Specific leaf area (m2 kg-1) * Average Transpiration (kg day-1) * Average % Extraction (The soil pot weight divided by saturated pot weight) * Total Transpiration (kg) water transpired over experiment * Average xylem vessel area (mm2) * Average xylem vessel density (#vessels mm-2) * Total Root weight (g) * root:shoot * Root length (cm) * Fraction Fine roots (%) * Fine root weight (g) * Leaf area:fine root * Water use efficiency (g biomass/kg water) * Transpiration divided by leaf area (ELA Kg day-1 m-2) * Predawn water potential (bars) * midday water potential (bars) * Leaf area:root length Missing data: N/A ## Code/software All the data files are MS Excel.  They can be viewed in Excel or google sheets.