DOI: 10.5061/dryad.tx95x6b8b
title: Data from: Volcanic soils alleviate the allelopathic capacity of Empetrum nigrum in degraded tundra ecosystems

description: Land degradation due to unsustainable land use is of major concern
 worldwide, and recovery is often slow. A potential mechanism behind slow
 recovery of degraded ecosystems is the retarding impacts of allelopathic
 plant species on the establishment of species that might facilitate the
 recovery process. However, the strength of the retarding impact may depend
 on soil type. In this study, we investigated the potential role of an
 abundant, evergreen, and allelopathic dwarf shrub, Empetrum nigrum, in
 trapping tundra ecosystems in a degraded state in Iceland after centuries
 of unsustainable land use. We first run a series of bioassays to assess
 the potential allelopathic legacy effects of the Empetrum-associated
 volcanic soils (Andosol and Vitrisol) on seed germination and root
 elongation of the common grass species Festuca richardsonii in comparison
 with Empetrum-associated non-volcanic Histosol and Podzol soil types. Then
 we assessed the Empetrum leaf-soil interactions for all soil types using
 leaves from a degraded site in Iceland. We found no potential allelopathic
 legacy effects of Empetrum associated with volcanic soils, whereas the
 non-volcanic soils negatively impacted Festuca root elongation. Empetrum
 leaves alone affected both seed germination and root elongation. These
 effects were strongly alleviated by the volcanic soils, but not by the
 non-volcanic soils. We conclude that abundant allelopathic plant species
 may significantly contribute to trapping tundra ecosystems in a degraded
 state, but the strength of this trapping mechanism depends on the soil
 environment.
description: # Data from: Volcanic soils alleviate the allelopathic capacity of
 *Empetrum nigrum* in degraded tundra ecosystems Dataset DOI:
 [10.5061/dryad.tx95x6b8b](10.5061/dryad.tx95x6b8b) ## 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 with and without the addition of leaves from the
 allelopathic dwarf shrub *Empetrum nigrum,* and different types and
 particle sizes of *Empetrum*-associated soil. ### Files and variables
 Inside the folder Ryde_et_al_2025.zip, there are six data files (.csv)
 accompanied by six code files (.R) used for statistical analyses. The file
 names, indicate which research question the data is related to (i.e. Q1 or
 Q2), which response variable was recorded (i.e. seed germination or
 seedling root elongation), and which soil particle size the seed or
 seedlings were incubated with (small or large soil particles). Code files
 are named similar to the data files they were analyzing.  **Meaning of
 column names and abbreviations within data files:** *Block:* Designates
 the experimental block that seeds and seedlings were located in during
 incubation and is used as random factor for statistical analyses. 
 *Dish:* Designates the Petri dish that seedlings were incubated in.
 Included as random factor when assessing the response variable root
 elongation.  *Soil type:* Indicates the different types of
 *Empetrum*-associated soil that seeds and seedlings were incubated with.
 Included as explanatory variable with the levels: A1, A2, H, V, P, and No
 soil. "No soil" refers to petri dishes to which no soil was
 added. In datasets where both "Soil type" and "Soil
 particles" occur, "No soil" is a confounding factor level
 of these two explanatory variables. Abbreviations: A1, Andosol 1; A2,
 Andosol 2;  H, Histosol; V, Vitrisol; P, Podzol. *Soil
 particles:* Indicates two different fractions of the soils, i.e. small
 (&lt; 1 mm) and large (&gt; 1 mm, &lt; 2 mm) soil particles. "No
 soil" refers to petri dishes to which no soil was added. Included as
 explanatory variable with the levels: Small, Large, and No soil, which is
 a confounding factor level with the explanatory variable "Soil
 type".  *Leaf addition:* Indicates the amount of *Empetrum* leaves in
 mg that were added to the petri dishes, which could be either no leaf
 addition (i.e. 0 mg) or leaf addition (&gt; 0 mg, i.e. 20 mg when
 assessing seedling root elongation and 130 mg when assessing seed
 germination). Included as explanatory variable with the levels: no leaf
 addition and leaf addition.  *Germination rate:* Recorded seed
 germination. Used as response variable.  *Root length:* Recorded seedling
 root length. Used as response variable.  **Description of files:**
 *Ryde_et_al_2025_Q1_Root elongation.csv* - Recorded root elongation of
 seedlings incubated with small and large soil particles from each soil
 type and no leaf addition.  *Ryde_et_al_2025_Q1_Root elongation.R* - R
 code used for statistical analysis of the recorded seedling root
 elongation, incubated with small and large soil particles from each soil
 type and no leaf addition.  *Ryde_et_al_2025_Q1_Seed germination.csv* -
 Recorded germination of seeds incubated with small and large soil
 particles from each soil type and no leaf addition. 
 *Ryde_et_al_2025_Q1_Seed germination.R* - R code used for statistical
 analysis of the recorded seed germination, incubated with small and large
 soil particles from each soil type and no leaf addition. 
 *Ryde_et_al_2025_Q2_Root elongation_Large soil particles.csv* - Recorded
 root elongation of seedlings incubated with large soil particles from each
 soil type and with and without leaf-addition.  *Ryde_et_al_2025_Q2_Root
 elongation_Large soil particles.R* - R code used for statistical analysis
 of the recorded seedling root elongation, incubated with large soil
 particles from each soil type and with and without leaf-addition. 
 *Ryde_et_al_2025_Q2_Root elongation_Small soil particles.csv* - Recorded
 root elongation of seedlings incubated with small soil particles from each
 soil type and with and without leaf-addition.  *Ryde_et_al_2025_Q2_Root
 elongation_Small soil particles.R* - R code used for statistical analysis
 of the recorded seedling root elongation, incubated with small soil
 particles from each soil type and with and without leaf-addition. 
 *Ryde_et_al_2025_Q2_Seed germination_Large soil particles.csv* - Recorded
 germination of seeds incubated with large soil particles from each soil
 type and with and without leaf-addition.  *Ryde_et_al_2025_Q2_Seed
 germination_Large soil particles.R* - R code used for statistical analysis
 of the recorded seed germination, incubated with large soil particles from
 each soil type and with and without leaf-addition. 
 *Ryde_et_al_2025_Q2_Seed germination_Small soil particles.csv* - Recorded
 germination of seeds incubated with small soil particles from each soil
 type and with and without leaf-addition.  *Ryde_et_al_2025_Q2_Seed
 germination_Small soil particles.R *- R code used for statistical analysis
 of the recorded seed germination, incubated with small soil particles from
 each soil type and with and without leaf-addition.  ## 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.