DOI: 10.5061/dryad.bzkh189kb
title: Photosynthetic induction and sunfleck responses of three shade-tolerant temperate saplings

description: Novel understory tree species composition has arisen throughout forests of
 the eastern U.S. as various, often human-caused, pressures have led to
 regeneration mismatch between trees in the forest canopy and
 understory.  Physiological attributes supporting the relative
 success of these novel understory tree communities are poorly
 characterized.  We sought to examine photosynthetic induction and
 sunfleck responses in three shade-tolerant understory tree species now
 common in the U.S.’s Mid-Atlantic region.  Focal species included
 the non-native Acer platanoides, as well as the natives Acer rubrum and
 Fagus grandifolia.  Three experiments were performed on three
 individuals of each species at three independent study sites in the
 broadleaf forests of southeastern Pennsylvania, USA.  The
 experiments were: (1) a photosynthetic induction experiment where
 uninduced leaves were first exposed to low light, followed by saturating
 light and measured until photosynthesis and stomatal conductance
 stabilized, (2) 30 second sunfleck experiments in which uninduced leaves
 were exposed to low light followed by a series of five 30 second
 saturating sunflecks, with two minutes of low light provided between each
 sunfleck, (3) 60 second sunfleck experiments in which uninduced leaves
 were exposed to low light followed by a series of five 60 second
 saturating sunflecks, with two minutes of low light provided between each
 sunfleck.  Findings show fairly similar and rapid photosynthetic
 induction responses among species, consistent with expectations for
 shade-tolerant tree species.  However, we observed a divergence
 in responses to applied sunflecks, where the two Acer species became
 induced more quickly than F. grandifolia and exhibited higher cumulative
 carbon assimilation when compared to conditions of constant saturating
 light.  This suggests the Acer species are well positioned to
 persist in the variable light environments of the forest understory.
description: A full description of the research methods is available in the
 associated published manuscript.  Three understory tree species,
 <em>Acer platanoides</em> (Norway maple), <em>Acer
 rubrum</em> (red maple), and <em>Fagus grandifolia</em>
 (American beech) were the focus of this study.  Three saplings per species
 at three southeastern Pennsylvania broadleaf forest study sites were
 measured.  Experiments were performed on different individual leaves per
 tree: (1) The first experiment was designed to measure the process of
 photosynthetic induction when leaves were uninduced (i.e., covered in
 light-blocking nylon bags), then exposed to low light (10 µmol
 m<sup>-2</sup> s<sup>-1</sup>) followed by
 saturating light (1000 µmol m<sup>-2</sup>
 s<sup>-1</sup>).  (2) Thirty second sunfleck experiments were
 also performed, in which uninduced leaves were exposed to low light
 followed by a series of five 30 second saturating sunflecks, with two
 minutes of low light provided between each sunfleck.  (3) Finally, a 60
 second sunfleck experiments was carried out, in which uninduced leaves
 were exposed to low light followed by a series of five 60 second
 saturating sunflecks, with two minutes of low light provided between each
 sunfleck.  Nine different attached leaves per species, spread evenly
 across three study sites were measured in each experiment.  In each
 experiment, leaves were measured with the LI-6800 infrared gas analyzer
 (LI-COR, Lincoln, NE), and measurements of photosynthesis, as well as
 stomatal conductance were recorded.  All leaves were collected following
 completion of measurements, scanned to determine fresh leaf area, dried to
 determine leaf dry mass, and analyzed to determine percent leaf nitrogen
 content.  In addition to leaf-level measurements, hemispherical
 photographs were taken adjacent to each sapling measured to determine
 global site factor (GSF) and percent canopy cover experienced by each
 study tree.
description: # Photosynthetic induction and sunfleck responses of three shade-tolerant
 temperate saplings 1. **Title of Dataset:** Photosynthetic induction and
 sunfleck responses of three shade-tolerant temperate saplings 2. **Author
 Information** A. Principal Investigator Contact Information Name: Jessica
 L. Schedlbauer Institution: West Chester University of Pennsylvania
 Address: Department of Biology, 730 S. Church St., West Chester, PA 19383,
 USA Email: [jschedlbauer@wcupa.edu](mailto:jschedlbauer@wcupa.edu) 3.
 **Date of data collection:** 2020-06-29 through 2020-07-28 4. **Geographic
 location of data collection:** Four sites in Chester County, PA, USA
 (Binky Lee Preserve (BLP): 40°05'42" N, 75°36'00" W;
 Gordon Natural Area (GNA): 39°56'08" N, 75°35'55" W;
 Mount Bradford Preserve (MBP): 39°56'33" N, 75°37'26"
 W, Miller Farm (MF): 40°01'54" N, 75°43'29" W) 5.
 **Information about funding sources that supported the collection of the
 data:** West Chester Univerisity's Department of Biology
 **SHARING/ACCESS INFORMATION** 1. **Links to publications that cite or use
 the data:** Schedlbauer, J.L. and S. Paynter. In review. Photosynthetic
 induction and sunfleck responses of three understory tree species in
 forests of the Mid-Atlantic U.S. Trees: Structure and Function (link will
 be added, pending article acceptance) 2. **Recommended citation for this
 dataset:** Schedlbauer, J.L. 2024. Photosynthetic induction and sunfleck
 responses of three shade-tolerant temperate saplings. (link will be added
 when available) **DATA & FILE OVERVIEW** 1. **File List:** *
 Hemispherical_photograph_data_2020.csv - file includes global site factor
 and percent canopy cover data for each tree used in the study *
 Leaf_data_2020.csv - file includes all measurements of leaf properties for
 each of the three experiments * Induction_trace_data_2020.csv - file
 includes all measurements of photosynthetic induction responses during
 exposure to constant saturating light * Sunfleck_30s_trace_data_2020.csv -
 file includes all measurements of leaf photosynthetic responses during
 exposure to artifically applied 30 second sunflecks *
 Sunfleck_60s_trace_data_2020.csv - file includes all measurements of leaf
 photosynthetic responses during exposure to artifically applied 60 second
 sunflecks 2. **Relationship between files:** All measurements were made at
 the same study sites in 2020. 3. **Date of file creation:** 2024-09-02
 **METHODOLOGICAL INFORMATION** 1. **Description of methods used for
 collection/generation of data:** See Schedlbauer and Paynter (In press)
 for detailed methodological information. In brief: Three experiments were
 performed on three individuals of three tree species at each of three
 different study sites. The experiments were (1) a photosynthetic induction
 experiment where uninduced leaves were first exposed to low light,
 followed by saturating light and measured until photosynthesis and
 stomatal conductance stabilized, (2) 30 second sunfleck experiments in
 which uninduced leaves were exposed to low light followed by a series of
 five 30 second saturating sunflecks, where 2 minutes of low light were
 provided between each sunfleck, (3) 60 second sunfleck experiments in
 which uninduced leaves were exposed to low light followed by a series of
 five 60 second saturating sunflecks, where 2 minutes of low light were
 provided between each sunfleck. Unique leaves were measured for each
 experiment and collected after measurment to determine leaf mass per unit
 area and leaf nitrogen content. Understory light conditions experienced by
 each tree were also measured via hemispherical photography. 2. **Methods
 for processing the data:** See the manuscript referenced above for
 details. **DATA-SPECIFIC INFORMATION FOR:
 Hemispherical_photograph_data_2020.csv** 1. **Number of variables:** 5 2.
 **Number of cases/rows:** 27 3. **Variable List:** * Site: Study site
 codes where BLP = Binky Lee Preserve, GNA = Gordon Natural Area, MBP =
 Mount Bradford Preserve, MF = Miller Farm * Species: Tree species codes
 where AB = American beech, NM = Norway maple, RM = red maple * Tree ID:
 unique identifier for each tree measured in the study * Global site
 factor: proportion of global radiation (direct plus diffuse radiation)
 reaching a given location, relative to a site with no obstructions *
 Percent canopy cover: calculated percent canopy cover, measured on the
 south side of each tree ~1 m from the edge of the tree's canopy and
 1.5 m above the soil surface **DATA-SPECIFIC INFORMATION FOR:
 Leaf_data_2020.csv** 1. **Number of variables:** 7 2. **Number of
 cases/rows:** 82 3. **Variable List:** * Experiment type: individual
 leaves from each tree were measured for each of the study's three
 experiments: Ind = induction experiment, SF30 = 30 second sunfleck
 experiment, SF60 = 60 second sunfleck experiment * Site: Study site codes
 where BLP = Binky Lee Preserve, GNA = Gordon Natural Area, MBP = Mount
 Bradford Preserve, MF = Miller Farm * Species: Tree species codes where AB
 = American beech, NM = Norway maple, RM = red maple * Tree ID: unique
 identifier for each tree measured in the study * LMA g/m2 (g/m2): grams of
 dry leaf mass per square meter of fresh leaf area * Percent nitrogen:
 percent nitrogen in each leaf, determined via elemental analysis * Narea
 g/m2 (g/m2): grams of nitrogen per square meter of fresh leaf area
 **DATA-SPECIFIC INFORMATION FOR: Induction_trace_data_2020.csv** 1.
 **Number of variables:** 11 2. **Number of cases/rows:** 10,258 3.
 **Variable List:** * Site: Study site codes where BLP = Binky Lee
 Preserve, GNA = Gordon Natural Area, MBP = Mount Bradford Preserve, MF =
 Miller Farm * Species: Tree species codes where AB = American beech, NM =
 Norway maple, RM = red maple * Tree ID: unique identifier for each tree
 measured in the study * Time elapsed (s): seconds elapsed after each
 induction experiment was initiated on an individual leaf * Photosynthesis
 (µmol CO2/m2/s): photosynthetic rate Ci (µmol CO2/mol air): leaf
 intercellular CO2 concentration * Stomatal conductance to water vapor (mol
 H2O/m2/s): rate of stomatal conductance to water vapor * Stomatal
 conductance to CO2 (µmol CO2/m2/s): rate of stomatal conductance to CO2 *
 Tleaf (degrees C): leaf temperature * VPD (kPa): leaf-to-air vapor
 pressure deficit * PAR (µmol photons/m2/s): applied photosynthetically
 active radiation 4. **Missing data:** Lines of data are missing from this
 file (blank) when the LI-6800 infrared analyzer indicated the presence of
 (1) a leak in the system, or when (2) the instrument recorded physically
 impossible Ci values. Also note, while data for Tree ID = 4 are included
 in this data file, they were excluded from the analysis presented in the
 published paper, as described therein. **DATA-SPECIFIC INFORMATION FOR:
 Sunfleck_30s_trace_data_2020.csv** 1. **Number of variables:** 11 2.
 **Number of cases/rows:** 11,772 3. **Variable List:** * Site: Study site
 codes where BLP = Binky Lee Preserve, GNA = Gordon Natural Area, MBP =
 Mount Bradford Preserve, MF = Miller Farm * Species: Tree species codes
 where AB = American beech, NM = Norway maple, RM = red maple * Tree ID:
 unique identifier for each tree measured in the study * Time elapsed (s):
 seconds elapsed after each sunfleck experiment was initiated on an
 individual leaf * Photosynthesis (µmol CO2/m2/s): photosynthetic rate * Ci
 (µmol CO2/mol air): leaf intercellular CO2 concentration * Stomatal
 conductance to water vapor (mol H2O/m2/s): rate of stomatal conductance to
 water vapor * Stomatal conductance to CO2 (µmol CO2/m2/s): rate of
 stomatal conductance to CO2 * Tleaf (degrees C): leaf temperature * VPD
 (kPa): leaf-to-air vapor pressure deficit * PAR (µmol photons/m2/s):
 applied photosynthetically active radiation **DATA-SPECIFIC INFORMATION
 FOR: Sunfleck_60s_trace_data_2020.csv** 1. **Number of variables:** 11 2.
 **Number of cases/rows:** 13,799 3. **Variable List:** * Site: Study site
 codes where BLP = Binky Lee Preserve, GNA = Gordon Natural Area, MBP =
 Mount Bradford Preserve, MF = Miller Farm * Species: Tree species codes
 where AB = American beech, NM = Norway maple, RM = red maple * Tree ID:
 unique identifier for each tree measured in the study * Time elapsed (s):
 seconds elapsed after each sunfleck experiment was initiated on an
 individual leaf * Photosynthesis (µmol CO2/m2/s): photosynthetic rate * Ci
 (µmol CO2/mol air): leaf intercellular CO2 concentration * Stomatal
 conductance to water vapor (mol H2O/m2/s): rate of stomatal conductance to
 water vapor * Stomatal conductance to CO2 (µmol CO2/m2/s): rate of
 stomatal conductance to CO2 * Tleaf (degrees C): leaf temperature * VPD
 (kPa): leaf-to-air vapor pressure deficit * PAR (µmol photons/m2/s):
 applied photosynthetically active radiation