Review Article |
Corresponding author: Chaeho Byun ( chaeho.byun@mail.mcgill.ca ) Academic editor: Montserrat Vilà
© 2024 Norul Sobuj, Kripal Singh, Chaeho Byun.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Sobuj N, Singh K, Byun C (2024) Responses of invasive and native plant species to drought stress and elevated CO2 concentrations: a meta-analysis. NeoBiota 96: 381-401. https://doi.org/10.3897/neobiota.96.132194
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Superior trait responses of invasive plant species to their native counterparts determine invasion success under various environmental conditions. To date, numerous experimental studies have compared the physiological and growth trait responses of invasive plant species to native ones in simulated drought or CO2 enrichment conditions; however, these studies have not recently been summarised. Here, we conducted a global meta-analysis using 48 experimental studies to determine whether there are generalisable differences between invasive and native plant species in terms of their physiological and growth trait responses to drought and elevated CO2 and which traits potentially facilitate plant invasion in these conditions. The results indicate that the magnitude of responses do not differ substantially between invasives and natives for most traits under drought or elevated CO2. Under drought stress, the photosynthetic rate, stomatal conductance, shoot biomass and total biomass decreased in both plant groups, supporting the contention that plants, irrespective of their origin, are negatively affected in water-limited environments. By contrast, we found that elevated CO2 increased water-use efficiency, shoot biomass and total biomass and decreased stomatal conductance in both invasives and natives, indicating that both plant groups grow vigorously in such conditions. Compared with estimates for natives, invasives were taller and invested more biomass to roots under drought and showed greater allocation to shoot biomass under elevated CO2. Although there were no substantial differences in the magnitude of responses in most studied traits, the differential growth responses in invasives may confer an advantage over natives under decreased water availability and high CO2 concentrations.
Effect size, environmental variation, invasion ecology, non-native plants, quantitative synthesis, trait-based comparison
Invasive plant species exert multifaceted effects on native biodiversity and many ecological processes (
Until recently, only a few studies compared the performance of invasive plant species and their native counterparts in various environmental conditions at a global scale (
Given the importance of understanding invasive-native trait divergence in the context of environmental variation, a good number of studies have focused on differences in physiological and growth trait responses between these two plant groups in stressful conditions (e.g.
The patterns in trait differences between invasive and native species may change with environmental conditions. It has widely been suggested that many invasive plant species will thrive in high-resource environments because invasive plant species, by virtue of their traits, tend to have fast resource use strategies and that attribute often becomes even faster in resource-rich non-native areas (
In this meta-analysis including the past and most recent literature data, we aim to compare the responses of invasive and native plant species in terms of their physiological and growth traits to drought stress and elevated CO2 concentrations. Although many different traits may determine the success of invasive plant species, we focused on a subset of traits associated with physiology (i.e. net photosynthetic rate, stomatal conductance and water-use efficiency) and growth (i.e. height, specific leaf area, shoot biomass, root biomass, total biomass and root-shoot ratio). We included only these above-mentioned traits in the current synthesis because these physiological and growth traits were more frequently investigated in the retrieved studies. Given the substantial importance of plant attributes in shaping invasion success in resident communities, if a consistent difference in various physiological and growth traits between these two plant groups can be identified where invasive species exhibit significantly higher values for a suite of traits than the native ones, this may provide insight into which traits potentially can facilitate plant invasions in drought stress and in environments with high CO2 concentrations in various ecosystems. We hypothesised that drought stress will constrain physiological and growth trait responses in both invasive and native plant species, but invasive species would still show greater tolerance to drought because of their higher plasticity and as they are more efficient at using limiting resources relative to native species adapted to such systems (
A literature survey was conducted to obtain peer-reviewed articles and thesis papers that report the responses of invasive and native plant species to drought stress and/or elevated CO2 concentrations. For the purpose of the current study, a ‘native’ plant species was defined as a species that is not invasive in the study area or elsewhere and an ‘invasive’ plant species was defined as a species that was introduced and became invasive in the study area. To retrieve a large sample of studies, Science Direct, PQDT (ProQuest Dissertations and Theses) Global, Springer Archive, Wiley Online Library, Oxford University Press, JSTOR (Biological Science), Proquest (Natural Science Collection) and Google Scholar were used as literature sources. The following keywords or phrases were used in various combinations to search for relevant papers: “climate change or environmental change or environmental fluctuation or environmental stress or extreme climatic event or drought or drought stress or water stress or precipitation variability or elevated carbon dioxide or elevated CO2 or carbon dioxide enrichment” AND “invasive or alien invasive or non-native invasive or non-native invasive” AND “native”. Relevant literature was also retrieved by scrutinising the reference lists of papers identified by this search and from prior meta-analyses conducted on the topic (
All retrieved studies were assessed individually. Studies were included in the meta-analysis if the following three criteria were met: 1) The study included at least one invasive and one native plant species in the same experiment. If a study involved several invasive and native plant species and they were not presented invasive-native pairwise, they were paired for the purpose of invasive-native comparison, based on their phylogenetic relatedness and/or shared growth forms. In some studies, several individual species were presented as an invasive or native plant group. Such groups were considered as an individual entity and included in the meta-analysis. All the experiments carried out in growth chambers, greenhouses, open top chambers (OTC), free air CO2 enrichment (FACE) systems, mesocosms and field conditions were included; 2) The experimental plants were exposed to at least two treatment levels (i.e. control and treatment) for drought stress or elevated CO2; 3) The study reported at least one of the following physiological or growth traits: net photosynthetic rate, stomatal conductance, water-use efficiency, specific leaf area, height, shoot biomass, root biomass, root-shoot ratio or total biomass of invasive and native plant species.
Mean values, sample sizes and variances (i.e. standard deviation or standard error) were extracted for the selected traits directly from texts or tables for all studies meeting the eligibility criteria. The web-based tool WebPlotDigitizer (
The effect sizes were computed and meta-analyses were performed using the MetaWin statistical programme (
To understand the overall mean effect of drought stress or elevated CO2 on a specific trait in invasive or native plant species, meta-analyses were conducted separately for each focal trait using the individual effect sizes and variances computed above. Mixed-effects models were preferred to perform the analyses with the assumption that there can be true random variation amongst the effect sizes originating from different studies (
Based on the study selection criteria, we identified 48 empirical studies published from 1991 to 2022 (Suppl. material
Mean effect sizes of drought stress on the physiological and growth trait responses of invasive and native plant species. Error bars represent 95% confidence intervals around the mean effect sizes. The numbers in parentheses indicate the number of studies included in the meta-analyses and the number of individual effect sizes used to calculate the mean effect sizes, respectively. Asterisks denote a statistically significant difference between invasive and native plant species and ms indicates a marginally significant difference.
Mean effect sizes of elevated CO2 concentrations on the physiological and growth trait responses of invasive and native plant species. Error bars represent 95% confidence intervals around the mean effect sizes. The numbers in parentheses indicate the number of studies included in the meta-analyses and the number of individual effect sizes used to calculate the mean effect sizes, respectively. Asterisks denote a statistically significant difference between invasive and native plant species and ms indicates a marginally significant difference.
Our meta-analyses indicate that drought stress had negative effects on physiological functions and growth performance in both invasive and native plant species (Fig.
Results of a meta-analysis of the effect of drought stress on the physiological and growth trait responses of invasive and native plant species. QB statistics and associated p-values for the difference in the magnitude of the response between invasive and native plant species subjected to drought stress are presented.
Trait | Species group | Effect sizes | Q B tests | ||||
---|---|---|---|---|---|---|---|
Mean | Lower 95% CI | Upper 95% CI | Q B | df | p | ||
Photosynthetic rate | Invasive | -0.32 | -0.55 | -0.09 | 0.28 | 1 | 0.599 |
Native | -0.40 | -0.61 | -0.19 | ||||
Stomatal conductance | Invasive | -1.73 | -2.45 | -0.99 | 0.84 | 1 | 0.359 |
Native | -2.14 | -2.65 | -1.64 | ||||
Specific leaf area | Invasive | 0.05 | -0.03 | 0.14 | 1.92 | 1 | 0.166 |
Native | -0.03 | -0.12 | 0.05 | ||||
Height | Invasive | -0.07 | -0.17 | 0.04 | 5.87 | 1 | 0.015 |
Native | -0.25 | -0.35 | -0.15 | ||||
Shoot biomass | Invasive | -0.48 | -0.65 | -0.31 | 2.69 | 1 | 0.101 |
Native | -0.68 | -0.86 | -0.51 | ||||
Root biomass | Invasive | -0.03 | -0.13 | 0.07 | 19.19 | 1 | 0.000 |
Native | -0.36 | -0.46 | -0.25 | ||||
Root-shoot ratio | Invasive | 0.09 | -0.02 | 0.20 | 3.56 | 1 | 0.059 |
Native | 0.25 | 0.13 | 0.36 | ||||
Total biomass | Invasive | -0.60 | -0.72 | -0.48 | 0.00 | 1 | 0.988 |
Native | -0.60 | -0.72 | -0.48 |
An elevated CO2 concentration promoted changes in the physiological and growth traits in both invasive and native plant species, irrespective of their origin (Fig.
Results of a meta-analysis of the effect of elevated CO2 concentrations on the physiological and growth trait responses of invasive and native plant species. QB statistics and associated p-values for the difference in the magnitude of response between invasive and native plant species subjected to elevated CO2 concentrations are presented.
Trait | Species group | Effect sizes | Q B tests | ||||
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Mean | Lower 95% CI | Upper 95% CI | Q B | df | p | ||
Photosynthetic rate | Invasive | 0.15 | 0.04 | 0.26 | 2.86 | 1 | 0.091 |
Native | 0.02 | -0.09 | 0.13 | ||||
Stomatal conductance | Invasive | -0.20 | -0.35 | -0.05 | 2.69 | 1 | 0.101 |
Native | -0.38 | -0.53 | -0.22 | ||||
Water use efficiency | Invasive | 0.23 | 0.08 | 0.39 | 0.19 | 1 | 0.660 |
Native | 0.19 | 0.03 | 0.34 | ||||
Specific leaf area | Invasive | -0.04 | -0.11 | 0.03 | 0.06 | 1 | 0.813 |
Native | -0.03 | -0.10 | 0.04 | ||||
Height | Invasive | 0.15 | 0.06 | 0.25 | 0.24 | 1 | 0.622 |
Native | 0.12 | 0.02 | 0.21 | ||||
Shoot biomass | Invasive | 0.52 | 0.45 | 0.59 | 11.43 | 1 | 0.001 |
Native | 0.31 | 0.22 | 0.41 | ||||
Root biomass | Invasive | 0.27 | 0.11 | 0.43 | 2.24 | 1 | 0.135 |
Native | 0.12 | -0.01 | 0.24 | ||||
Root-shoot ratio | Invasive | 0.10 | -0.01 | 0.21 | 0.20 | 1 | 0.653 |
Native | 0.16 | -0.07 | 0.40 | ||||
Total biomass | Invasive | 0.28 | 0.19 | 0.36 | 2.33 | 1 | 0.127 |
Native | 0.18 | 0.10 | 0.27 |
We predicted that both invasive and native plant species would show decreased performance in response to drought stress. Our meta-analysis indicated that the photosynthetic rate, stomatal conductance, shoot biomass and total biomass decline significantly in both groups of plants growing under reduced water availability. These results are consistent with numerous earlier studies showing that, when invasive and native plant species of various growth forms are subjected to simulated drought stress, they decrease their physiological functions, including photosynthetic carbon assimilation and stomatal conductance (
We further hypothesised that the negative effects of drought stress will be greater for natives than for invasive species. Our results showed that, while invasive and native plant species were similar with respect to most traits under drought conditions, natives had significantly lower height growth and root biomass production when compared to their invasive counterparts. This indicates that invasive species were taller and invested more biomass into below-ground growth than did native species in environments with decreased water availability. For invasive species, modifications in biomass allocation could be beneficial under drought conditions. Increased allocation to the root system could be a key adaptation mechanism for the invasive species in decreased water availability, because roots can strongly affect water and nutrient acquisition in plants (
Contrary to our expectation, significant performance differences between invasive and native plant species existed only in height growth and root biomass production amongst the eight physiological and growth traits we analysed in response to drought stress. Therefore, strong evidence for invasive plant species differing substantially from native species in water-limited environments was lacking. We argue that, if the variation exists in only two traits, as was found in this global meta-analysis in height and root biomass between invasive and native plant species, it is unlikely that invasives will outcompete natives based solely as a result of these response differences in drought conditions. Our findings are consistent with those of earlier studies (e.g.
Fitting with our expectation, CO2 enrichment promoted physiological processes and growth changes in both invasive and native plant species. We found that, irrespective of species origin, plants grown in environments with a high CO2 concentration had considerably higher water-use efficiency, shoot biomass and total biomass. Our results also demonstrate that stomatal conductance decreased significantly in both species groups subjected to elevated CO2 concentrations. Reduced stomatal conductance may have contributed to the increased instantaneous water-use efficiency under elevated CO2 concentrations, as observed previously in many species, including invasives and natives grown at high CO2 concentrations (
Many earlier studies underlined the success of invasive species as a function of invasive-native performance differences across various conditions, such as environments with high CO2 concentrations, high soil nutrients or ample water availability (e.g.
Our findings are surprising considering that invasive plant species are presumably more successful than their native counterparts on a global scale and in high resource environments. Numerous empirical studies previously found a divergence in responses between invasive and native plant species to elevated CO2 concentrations in a long suite of traits including photosynthetic rate, stomatal conductance, specific leaf area, height, root biomass, total biomass and reproduction (
Our findings do not provide a clear indication whether invasive plant species will dominate over natives in drought stress or elevated CO2 concentrations. We acknowledge some limitations associated with this synthesis. First, most of the plant species included in this study were herbaceous (86%) (Suppl. material
Moreover, the majority of the studies included in this meta-analysis were short-term, mostly lasting one growing season (90%) (Suppl. material
Finally, we did not evaluate various traits, such as reproduction, survivorship, allelopathy and susceptibility to herbivory, owing to limited data availability and these traits may differ between invasive and native plant species in environments with decreased water availability or high CO2 concentrations (
The findings of this meta-analysis indicate that drought stress suppresses the performance of both invasive and native plant species, while an elevated CO2 concentration stimulates physiological processes, except stomatal conductance and growth traits in both plant groups. Our results also indicate that, compared with native plant species, invasive species had a significantly greater height growth and invested more biomass to below-ground root system in drought conditions and had a greater allocation to above-ground biomass production in elevated CO2 concentrations. These differential responses of invasive plant species in growth traits may provide them with an advantage in adaptation over native species under decreased water availability and CO2 enrichment. However, the magnitude of responses in most traits did not differ substantially between invasive and native plant species, indicating that invasive species are unlikely to outcompete natives in these altered environmental conditions. This certainly does not mean that invasive species will not be pervasive in the future, as they are capable of greater allocation to below-ground and above-ground biomass production compared with that of native counterparts under variable environments. Still, we need to be careful when predicting a bleak future regarding intensive dominance of invasive plants across different environmental conditions.
The authors have declared that no competing interests exist.
No ethical statement was reported.
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) (2022R1A2C1003504).
NS and CB conceptualised and designed the study; NS extracted and analysed the data and developed graphs and tables; NS wrote the first draft of the original manuscript; KS and CB reviewed and edited the manuscript. All authors approved the submission to the journal.
Norul Sobuj https://orcid.org/0000-0002-2594-6690
Kripal Singh https://orcid.org/0000-0003-2845-7160
Chaeho Byun https://orcid.org/0000-0003-3209-3275
Datasets were shared in the open access file directories of Figshare https://doi.org/10.6084/m9.figshare.27924888.
Additional information
Data type: docx
Explanation note: table S1. Overview of the experimental studies included in the meta-analysis. fig. S1. Funnel plot representing the relationship between effect size (lnR) and the inverse of the standard error (SE) in drought stress. fig. S2. Funnel plot representing the relationship between effect size (lnR) and the inverse of the standard error (SE) in elevated CO2 concentration.