Data from: Temperature dependence of pollen germination and tube growth in conifers relates to their distribution along an elevational gradient in Washington State, USA
Data files
Jun 17, 2026 version files 4.91 MB
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Polle_site_temperature.csv
2.88 MB
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Pollen_and_HOBO_locations.csv
4.02 KB
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Pollen_GP.csv
87.53 KB
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Pollen_TL.csv
1.93 MB
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README.md
6.07 KB
Abstract
Background and Aims
Pollen germination and tube growth are essential processes for successful fertilization. They are among the most temperature-vulnerable stages and subsequently affect seed production and determine population persistence and species distribution under climate change. Our study aims to investigate intra- and interspecific variations in the temperature dependence of pollen germination and tube length growth and to explore how these variations differ for pollen from elevational gradients.
Methods
We focused on three conifer species, Pinus contorta, Picea engelmannii and Pinus ponderosa, with pollen collected from 350 to 2200 m elevation in Washington State, USA. We conducted pollen viability tests at temperatures from 5 to 40 °C in 5 °C intervals. After testing for 4 d, we took images of these samples under a microscope to monitor pollen germination percentage (GP) and tube length (TL). We applied the gamma function to describe the temperature dependence of GP and TL and estimated key parameters, including the optimal temperature for GP (Topt_GP) and TL (Topt_TL).
Key Results
Results showed that pollen from three species and different elevations within a species have different GP, TL, Topt_GP, and Topt_TL. The population with a higher Topt_GP would also have a higher Topt_TL, while Topt_TL was generally higher than Topt_GP, i.e. a positive but not one-to-one relationship. However, only Pinus contorta showed that populations from higher elevations have lower Topt_GP and Topt_TL and vice versa. The variability in GP increased at extreme temperatures, whereas the variability in TL was greatest near Topt_TL.
Conclusions
Our study demonstrates the temperature dependences of three conifers across a wide range of temperatures. Pollen germination and tube growth are highly sensitive to temperature conditions and vary among species and elevations, affecting their reproduction success during warming. Our findings can provide valuable insights to advance our understanding of how conifer pollen responds to rising temperatures.
Dataset DOI: 10.5061/dryad.g79cnp660
Description of the data and file structure
Pollen germination and tube growth are essential processes for successful fertilization. They are among the most temperature-vulnerable stages and subsequently affect seed production and determine population persistence and species distribution under climate change. Our study aims to investigate intra- and interspecific variations in the temperature dependence of pollen germination and tube length growth and to explore how these variations differ for pollen from elevational gradients. We focused on three conifer species, Pinus contorta, Picea engelmannii and Pinus ponderosa, with pollen collected from 350 to 2200 m elevation in Washington State, USA. We conducted pollen viability tests at temperatures from 5 to 40 °C in 5 °C intervals. After testing for 4 d, we took images of these samples under a microscope to monitor pollen germination percentage (GP) and tube length (TL). We applied the gamma function to describe the temperature dependence of GP and TL and estimated key parameters, including the optimal temperature for GP (Topt_GP) and TL (Topt_TL). See the Material & Methods section in the corresponding manuscript for a more detailed description for data collection and analysis.
Works referencing this dataset:
Hsu, Hsin-Wu, and Soo-Hyung Kim. "Temperature dependence of pollen germination and tube growth in conifers relates to their distribution along an elevational gradient in Washington State, USA." Annals of Botany 135.1-2 (2025): 277-292. https://doi.org/10.1093/aob/mcae079
Files and variables
File: Pollen_and_HOBO_locations.csv
Description: Longitude, latitude, and elevation of pollen collection sites and HOBO temperature sensors. 86 rows x 6 columns
Variables
- No.: Pollen sample number and HOBO sensor number. TM: Tyee Mountain; SP: Slate Peak
- Species: PICO : Pinus contorta; PIEN: Picea engelmannii; PIPO: Pinus ponderosa; HOBO: HOBO temperature sensor
- X: Longitude
- Y: Latitude
- Elevation (m): Elevation in meters
- Date: Pollen collection date or HOBO deployment date (month/day/year)
File: Polle_site_temperature.csv
Description: A data file (93375 rows x 4 columns) containing hourly temperatures at pollen collection sites.
Variables
- Site: Pollen collection sites. TM: Tyee Mountain; SP: Slate Peak
- Elevation: The elevation of the location of HOBO temperature sensors. Unit: meters
- Date: date and time (month/day/year/hour) when the temperature was recorded.
- Temperature: air temperature; Unit: °C
File: Pollen_GP.csv
Description: A data file (3117 rows x 8 columns) containing pollen germination of three conifer species under different temperatures.
Variables
- Species: PICO: Pinus contorta; PIEN: Picea engelmannii; PIPO: Pinus ponderosa
- Temperature: Pollen incubation temperatures from 5 to 40 degrees Celsius with an interval of 5°C
- Elevation: Pollen collection elevations; unit: meters
- Replicate: The test round of pollen germination from rounds one to three. There is one vial in each round.
- Subsample: The sample collected in each round, i.e., samples collected from each vial. Two subsamples in each round.
- Pollen COUNTED: The number of pollens counted in each subsample. Normally, we counted 200 pollens. However, in some situations, there was not enough pollen. The numbers showed how many pollens we actually counted.
- Pollen germinated: The number of pollen grains that germinated was counted in the previous column (Pollen COUNTED). NA: no data
- GP: Pollen germination = (Pollen germinated/Pollen COUNTED) x 100; unit: %). NA: no data
File: Pollen_TL.csv
Description: A data file (62401 rows x 7 columns) containing pollen tube length of three conifer species under different temperatures.
Variables
- Species: PICO: Pinus contorta; PIEN: Picea engelmannii; PIPO: Pinus ponderosa
- Temperature: Pollen incubation temperatures from 5 to 40 degrees Celsius with an interval of 5°C
- Elevation: Pollen collection elevations; unit: meters
- Replicate: The test round of pollen germination from rounds one to three. There is one vial in each round.
- Subsample: The sample collected in each round, i.e., samples collected from each vial. Two subsamples in each round.
- Pollen_no: The specific index number of the individual pollen tube measured. Normally, we measured 20 pollen tube lengths. If fewer than 20 pollen grains germinated, we measured the number of germinated pollen grains.
- Length: Pollen tube length. Unit: nm. NA: no data
Code/software
The ‘AIC’ function in the ‘stats’ package (R Core Team, 2021) was used to calculate AIC values. We used simple linear regression to fit (1) the observed GP and TL to different elevations within the same species and tested temperature, and (2) the Topt_GP and Topt_TL to different elevations within the same species to test H1 and H2. We also used a one-way analysis of variance (ANOVA) and Tukey’s honest significance test to test the Topt_GP and Topt_TL among species (H2). A t-test was used to compare the differences between each species’ Topt_GP and Topt_TL, and the ‘emtrends’ function in the ‘emmeans’ package (Lenth, 2022) was used to test the one-to-one relationship between Topt_GP and Topt_TL (H3). A quadratic function was used to fit the coefficient of variation in each species and temperature. The monthly mean temperature along the elevational gradients at Tyee Mountain and Slake Peak was calculated. We then used simple linear regression to estimate the lapse rate of each month and site. All analyses were conducted in the R 4.1.2 programming language (R Core Team, 2021).