DOI: 10.5061/dryad.73n5tb38z
title: Intra-specific variability and sex influence the allelopathic capacity of Empetrum nigrum

description: 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.
description: # Intra-specific variability and sex influence the allelopathic capacity
 of *Empetrum nigrum* Dataset DOI:
 [10.5061/dryad.73n5tb38z](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.