Intra-specific variability and sex influence the allelopathic capacity of Empetrum nigrum
Data files
Aug 01, 2025 version files 17.85 KB
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README.md
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Ryde_et_al._2025.zip
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Abstract
Allelopathic plant species play significant roles in shaping natural ecosystems. While a high degree of inter-species variation in allelopathic capacities is commonly reported, variation across intra-specific groups and between dioecious sexes is limited. Here we use the ecologically important, allelopathic dwarf shrub Empetrum nigrum L. to assess how allelopathic capacity varies between intra-specific groups (i.e., the diploid and dioecious “nigrum” group and the tetraploid and synoecious “hermaphroditum” group of Empetrum) and sex (i.e., male and female plants of the nigrum group). Specifically, we tested Icelandic Empetrum, as its allelopathic nature may influence long-term land degradation across Icelandic highlands. The allelopathic capacity of Empetrum leaves was measured in a series of bioassays as the inhibition of seed germination and seedling root elongation of the grass Festuca richardsonii. A very strong allelopathic response of Empetrum leaves was observed. Intra-specific and sex-related differences in allelopathic capacity were also detected, with the hermaphroditum group possessing a greater germination inhibitory effect compared to the nigrum group, and males of the nigrum group inhibited germination more than females. Targeted liquid chromatography-mass spectrometry (LC-MS) quantification of two known Empetrum allelopathic constituents – Batatasin-III (BIII) and 3,4-dimethoxy-2´,5-dihydroxybibenzyl (DDB) – showed that BIII concentrations were significantly higher in leaves from the hermaphroditum group compared to the nigrum group, but no differences were observed between males and females within the nigrum group. DDB was not detected in the sampled Icelandic Empetrum populations. Our results indicate that Empetrum may differentially impact plant interactions and ecosystem processes depending on the relative abundance of Empetrum intra-specific groups and sexes within populations, and that BIII is not solely responsible for the allelopathic capacity of Icelandic Empetrum.
Dataset DOI: 10.5061/dryad.73n5tb38z
Description of the data and file structure
The data files contain recordings of germination and root elongation of the grass species Festuca richardsonii seeds and seedlings, incubated in bioassays with different amounts of leaves from three different intra-specific groups and sexes of the dwarf shrub Empetrum nigrum: the “hermaphroditum” group, and male and female sexes of the “nigrum” group. There is also a data file of foliar concentrations of the previously designated key allelochemical Batatasin-III (BIII), assessed in the leaf material used for the bioassays.
Files and variables
Inside the folder Ryde_et_al._2025.zip, there are eight data files (.csv) accompanied by eight code files (.R) used for statistical analyses. Code files are named similarly to the data files they were analyzing.
Meaning of column names and abbreviations within data files:
Germination: Recorded seed germination (/10). Used as a response variable in statistical models when assessing allelopathic effects on seed germination.
Root length: Recorded root length (mm) after end incubation of pre-germinated seeds (having 2 mm root when added to the petri dishes). Used as a response variable in statistical models when assessing allelopathic effects on seedling root elongation.
Block: Designates the experimental block (#) that seeds and seedlings were located in during incubation. Included as a random factor for statistical analyses, when assessing the response variables, seed germination, and seedling root elongation.
Dish: Designates the Petri dish (#) that seedlings were incubated in. Included as a random factor for statistical analyses when assessing the response variable root elongation.
Empetrum group: Designates from what Empetrum group (hermaphroditum, male nigrum, or female nigrum) the leaves, which were added to petri dishes to assess allelopathic capacity or analyzed for BIII concentrations, originated from. Included in statistical models as an explanatory variable.
Leaf DW: The leaf dry weight (mg) of the seeds or seedlings was incubated with. Included as an explanatory variable when assessing the response variables, seed germination, and seedling root elongation.
Day: Indicates on what incubation day (#) the recordings of seed germination were done, which was 10 days in total over an incubation period of 31 days. Included as an explanatory variable when assessing the response variable seed germination.
Sample DW: The dry weight (g) of the leaf sample used for BIII quantification. Used to calculate BIII concentrations in the unit: mg BIII g^-1 dry weight leaf sample.
Caffeine: The measured compound signal (peak area) of the internal standard caffeine. Used to normalise the calculated BIII concentrations before statistical analyses.
BIII: The calculated BIII concentrations (mg BIII g^-1 dry weight leaf-sample).
BIII normalized: The normalized BIII concentrations, i.e., the BIII concentration was divided by the caffeine compound signal. Used as a response variable when analyzing differences in BIII concentrations between the different Empetrum groups.
Description of files:
Ryde et al. 2025_Foliar BIII concentrations of different Empetrum groups and sexes.csv - BIII concentrations quantified in leaves from the different Empetrum groups and the normalized BIII concentrations used for statistical analyses.
Ryde et al. 2025_Foliar BIII concentrations of different Empetrum groups and sexes.R - R code used to analyze how the normalized BIII concentrations vary between the different Empetrum groups.
Ryde et al. 2025_Inhibitory effects of Empetrum leaves on seed germination.csv - Recorded germination of seeds incubated with leaves from the different Empetrum groups.
Ryde et al. 2025_Inhibitory effects of Empetrum leaves on seed germination.R - R code used for statistical analyses of how leaves from the different Empetrum groups affect seed germination differently.
Ryde et al. 2025_Inhibitory effects of high Empetrum leaf dry weights on seedling root elongation. csv - Recorded root elongation of seedlings incubated with high amounts of leaves, i.e., “high leaf dry weights”, from the different Empetrum groups. Seedling root elongation was recorded once after the end of incubation.
Ryde et al. 2025_Inhibitory effects of high Empetrum leaf dry weights on seedling root elongation. R - R code used for statistical analyses of how high amounts of leaves from the different Empetrum groups affect seedling root elongation differently.
Ryde et al. 2025_Inhibitory effects of low Empetrum leaf dry weights on seedling root elongation. csv - Recorded root elongation of seedlings incubated with low amounts of leaves, i.e., “low leaf dry weights”, from the different Empetrum groups. Seedling root elongation was recorded once after the end of incubation.
Ryde et al. 2025_Inhibitory effects of low Empetrum leaf dry weights on seedling root elongation. R - R code used for statistical analyses of how high amounts of leaves from the different Empetrum groups affect seedling root elongation differently.
Code/software
R version 4.3.3 was used for coding. In the R software, the lme4 package was used to establish mixed-effects models, the MASS package was used to do model validation, and the emmeans package was used to do pairwise comparisons.