DOI: 10.5061/dryad.8sf7m0d2q
title: Interspecific competition negates CO₂ benefits for most plant species

description: Elevated CO₂ (eCO₂) frequently increases plant growth and primary
 productivity, and is considered a driver of increased land carbon sinks.
 This evidence contributes to a widespread but surprisingly untested
 assumption in global change science and policy, and society at large, that
 eCO₂ consistently stimulates the growth of plant species within
 communities. However, species and community responses depend on species’
 growth strategies and abiotic and biotic contexts, and among these, the
 role of competition remains underexplored. We therefore ask whether eCO2
 enhances growth broadly across species, or primarily in a dominant few? To
 address this question of how species interactions are shaped by eCO₂
 response and competitive ability, we analysed responses from 97 species in
 20 grassland CO₂ enrichment experiments. Herein, we show that
 interspecific competition markedly reduced eCO₂ stimulation: while most
 species responded positively to eCO₂ in isolation, over half responded
 negatively in mixed communities. Despite this, community biomass was often
 and on average was increased under eCO₂, driven by dominant species
 contributions. eCO₂ did not enhance competition tolerance, and acquisitive
 traits—including fast growth and invasion success—conferred a consistent
 advantage under both CO₂ enrichment and competitive stress. Our findings
 suggest that in species mixtures, which represent the majority of natural
 ecosystems, competition causes both positive and negative growth responses
 to eCO2 to be ubiquitous and pervasive. We show that eCO₂ does not
 consistently reduce competitive vulnerability, but instead, trait-based
 filtering in a competitive context determines both which species benefit
 from eCO2. These results challenge assumptions built into ecosystem
 models; and incorporating these dynamics will improve forecasts of
 vegetation response to rising CO₂.
description: # Interspecific competition negates CO₂ benefits for most plant species ##
 Overview This repository contains the R code and datasets used to generate
 Figures 2, 3, and 4 for the manuscript *Interspecific competition negates
 CO₂ benefits for most plant species* (Raubenheimer et al., 2026, Nature
 Plants revision). All analyses are run from a single master script and
 reproduce all figures and supplementary tables. ## Repository structure
 /Data/ MetaAnalysis_Data5.csv MetaAnalysis_Data6.csv Sum_Of_Mix.csv
 Traits2.csv /Code/ RCode.R README_DRYAD.Rmd README.md ## Dataset variable
 definitions ### MetaAnalysis_Data5.csv Description: Species-level biomass.
 Cells with 'NA' represent where a value is not applicable
 (rather than just missing). Note where 'CO2' is abbreviated in
 the variables; this refers to carbon dioxide. Variables: | Column |
 Description | Units / Notes | |--------|-------------|----------------| |
 X | Row index | — | | Species | Scientific name | matches Traits2.csv | |
 Species.Status.FunctMetab | Functional type | character | |
 Neighbours.FunctMetab | Functional type of neighbours | character | |
 Competition.Treatment | Competition treatment | Isolated / Monoculture /
 Inter-Functional Mixture / Intra-Functional Mixture | | CO2.Treatment |
 CO₂ treatment | High_CO2 / Low_CO2 | | CO2.Treatment.Value | CO₂ ppm |
 numeric | | Plant.age..days. | Plant age | days | |
 Length.of.CO2.exposure..days. | Duration of CO₂ exposure | days | |
 Method.of.CO2.Treatment | CO₂ enrichment method | categorical | | Paper |
 Study name | short citation | | Biome.Category | Biome type | categorical
 | | Location | Study location | character | | Continent | Continent |
 character | | Dominance.ratio | Dominance metric | unitless | |
 Sum.of.mixture | Total mixture biomass | g | | Biomass | Mean biomass of
 focal species | g | | SE | Standard error | g | | RCV.RR | Response ratio
 of RCV | unitless | | yi_RCV | Effect size for RCV | unitless | | vi_RCV |
 Variance of yi_RCV | unitless | | yi_CO2 | Effect size for CO₂ | unitless
 | | vi_CO2 | Variance of yi_CO₂ | unitless | **Variable names that are
 created in the code:** | Variable | Description | Units | Notes |
 |--------|-------------|----------------|----------------| | Method |
 Experimental method | categorical | (this was Method.of.CO2.Treatment in
 the dataframe) | | Duration | Duration of experiment | days | (this was
 Length.of.CO2.exposure..days. in the dataframe) | | Comp | Harmonised
 competition variable | used in modelling | (this was Competition.Treatment
 in the dataframe) | | FT | Harmonised functional type | used in modelling
 | (this was Species.Status.FunctMetab in the dataframe) | ###
 Sum_of_Mix.csv Description: Community-level biomass. Values are in the row
 of one species per community (i.e., NAs for the other species in the same
 community. Species names are not relevant in the code - values are taken
 according to each study and treatment). Cells with 'NA'
 represent where a value is not applicable (rather than just missing). Note
 where 'CO2' is abbreviated in the variables; this refers to
 carbon dioxide. Variables: | Column | Description | Units / Notes |
 |--------|-------------|----------------| | FT | Functional type |
 character | | Neighbours.FT | Neighbour functional type | character | |
 Comp | Competition treatment | Mono / Mix | | CO2.Treatment | CO₂
 treatment | High_CO2 / Low_CO2 | | CO2.Treatment.Value | ppm | numeric | |
 Plant.age..days. | Age | days | | Duration | Duration | days | | Method |
 Treatment method | categorical | | Paper | Study name | character | |
 Biome.Category | Biome | character | | Location | Location | character | |
 Continent | Continent | character | | Sum.of.community | Community biomass
 | g | | CO2.Effect | Log response ratio | unitless | | n | Sample size | —
 | | mean_SE | Mean SE | — | | yi_Mix | Effect size | unitless | | vi_Mix |
 Variance | unitless | ### MetaAnalysis_Data6.csv Same structure as
 MetaAnalysis_Data5, but includes: **Variable names that are created in the
 code:** | Column | Description | |--------|-------------| | No.of.species
 | Number of species in community | | X2 | Dominance ratio duplicate column
 | legacy | | Dominance.ratio, Sum.of.mixture, Biomass, SE | As above | ###
 Traits2.csv Description: Trait values acquired from the TRY database,
 AusTraits, and references manuscripts. Unused variables are left in the
 dataset to avoid issues with column numbers in the accompanying code.
 Empty cells in the Traits2.csv data represent where trait data was not
 available for a given species. These empty cells are important for the
 code that imputes trait data. Variables: | Column | Description | Units |
 | ---------------------- |
 -------------------------------------------------- | --------------------
 | | Species | Scientific name | — | | Paper | Source study | — | |
 Neighbours.Combo | Functional group of neighbouring species | categorical
 | | Neighbour.Species | Name of neighbouring species | categorical | | X2
 | (unused column) | — | | X3 | (unused column) | — | | X4 | (unused
 column) | — | | X5 | (unused column) | — | | X6 | (unused column) | — | |
 X7 | (unused column) | — | | Species.Status | Functional type (e.g., C3
 herbaceous) | categorical | | Species.Status.Broad | Broad functional
 grouping | categorical | | Leaf.area | Leaf area | cm² | | Nmass | Leaf
 nitrogen concentration | mg g⁻¹ | | LMA | Leaf mass per area | g m⁻² | |
 Plant.height | Plant height | m | | Diaspore.mass | Mass of dispersal unit
 (seed/fruit) | mg | | LDMC | Leaf dry matter content | mg g⁻¹ | | SSD |
 Stem specific density | g cm⁻³ | | database | Data source / database |
 categorical | | SLA | Specific leaf area | mm² mg⁻¹ or cm² g⁻¹ | | LeafN |
 Leaf nitrogen | % | | LeafC | Leaf carbon | % | | LeafCN | Leaf
 carbon:nitrogen ratio | unitless | | Root.Shoot | Root:shoot biomass ratio
 | unitless | | Light.Rating | Shade / light tolerance rating | categorical
 (1–10) | | Moisture.Rating | Soil moisture requirement | categorical
 (1–10) | | Ellenberg.light | Ellenberg light indicator | categorical
 (1–12) | | Ellenberg.moisture | Ellenberg moisture indicator | categorical
 (1–12) | | Ellenberg.pH | Ellenberg soil pH indicator | categorical | |
 Ellenberg.N | Ellenberg nutrient indicator | categorical | |
 Ellenberg.salt | Ellenberg salinity indicator | categorical | |
 Ellenberg.temperature | Ellenberg temperature indicator | categorical | |
 Ellenberg.humidity | Ellenberg humidity indicator | categorical | |
 Growth.Form | Growth form (herb, shrub, tree, etc.) | categorical | |
 Lifespan.years | Lifespan | years | | Growing.Speed | Growth rate class |
 categorical | | Height | Maximum plant height | mm | | Grime.strategy |
 CSR strategy (Competitor–Stress Tolerator–Ruderal) | categorical | |
 Lifespan | Lifespan | years | | Pollination | Pollination syndrome |
 categorical | | Pollinator | Pollinator type | categorical | | Propagation
 | Propagation type | categorical | | Resprout.ability | Ability to
 resprout after disturbance | categorical (yes/no) | | Shade.tolerant |
 Shade tolerance | categorical | | Classified.as.invasive | Invasive status
 | categorical (yes/no) | | Cold.Tolerant | Cold tolerance | categorical |
 | Fire.tolerant | Fire tolerance | categorical | | Drought.tolerant |
 Drought tolerance | categorical | ## Figure Summaries - Figure 2:
 Species-level responses to CO₂ × competition - Figure 3: Community-level
 biomass responses and dominance ratios - Figure 4: Trait-based DAPC and
 LMM analyses ## Execution Instructions 1. Place all data in `/Data/` 2.
 Open `RCode.R` 3. Run figure sections sequentially 4. All outputs saved to
 `/R_out/` ## 6. Code and Software All coding is done using the R software
 package (R Core Team (2024). \_R: A Language and Environment for
 Statistical Computing_. R Foundation for Statistical Computing, Vienna,
 Austria. [https://www.R-project.org/](https://www.R-project.org/).)
 '#' is used throughout the code to label actions. ## Session
 Information R version 4.5.0 (2025-04-11) Platform: aarch64-apple-darwin20
 Running under: macOS 26.2 Matrix products: default BLAS:
 /System/Library/Frameworks/Accelerate.framework/... LAPACK:
 /Library/Frameworks/R.framework/... *(Full session info retained exactly
 as provided.)* ## Data Provenance & Ethics Data collection: Compiled
 from published experimental studies on plant CO₂ responses and trait
 measurements. Full study list in manuscript references. Ethics: No human
 subject data. No sensitive location data for threatened species. Special
 formatting: No merged cells, highlighting, or other special formatting are
 used in the provided tabular data files. ## Related Resources Manuscript
 DOI: to be added upon acceptance Dryad DOI: to be assigned upon upload
 Source datasets cited in manuscript reference list. ## Reproducibility
 Notes All figures can be reproduced using the RCode.R script provided,
 which contains self-contained code blocks for each figure. Ensure all CSV
 files are placed in the /Data/ directory as expected by the script.
 Outputs are saved automatically to /R_out/. No manual steps are required
 between figures.