1 Introduction
Global surface temperatures have risen rapidly since the Industrial Revolution, with projections suggesting an increase of 1.5°C between 2030 and 2052, and up to 3°C by 2100 (
Masson-Delmotte et al., 2022). This rapid warming significantly alters terrestrial carbon (C) cycling, which, in turn, affects climate feedbacks that may either amplify or mitigate future warming (
Heimann and Reichstein, 2008;
Fang et al., 2018). While understanding the impacts of warming on terrestrial ecosystem C cycling is critical, substantial uncertainties persist in modeling and predicting ecosystem C fluxes under future warming scenarios (
Friedlingstein, 2015;
Xia and Lu, 2020;
Yuan et al., 2024). Much of this uncertainty stems from our limited knowledge of vegetation responses and their feedbacks to climate change.
Warming influences CO
2 fluxes not only by modifying environmental factors such as temperature and moisture, but also by altering plant communities, both of which are critical drivers of C cycling (
Cahoon et al., 2012;
Mekonnen et al., 2018). However, most studies focused primarily on environmental factors, usually neglecting vegetation dynamics (
Ward et al., 2013), which introduces substantial biases in modeling C fluxes and predicting future climate trajectories.
Quantifying warming-induced changes in plant communities and linking these changes to ecosystem CO
2 fluxes remains a key challenge. Current approaches relying on plant functional groups often produce inconsistent results: the same functional group may respond differently across studies, and species within a group can exhibit divergent responses (
Alatalo et al., 2020;
Hu et al., 2021). In addition, some modeling studies have also found that plant functional type (PFT)-based parameterizations usually fail to capture the substantial variability in processes within the same PFT (
Yang et al., 2021;
Ren et al., 2025). Thus, the use of functional types in models predicting the C cycle under climate warming may introduce considerable uncertainty.
Plant traits, as measurable characteristics that reflect plants’ long-term responses and adaptations to environmental changes, offer a robust framework. Species with contrasting traits respond differently to climate change, driving shifts in community composition and structure (
Wang et al., 2017;
Xiao et al., 2021). These shifts, in turn, alter community-level traits, which directly drive ecosystem C cycling and feedback (
Gross et al., 2017;
Bjorkman et al., 2018). This trait-based approach offers two key advantages: (i) it reveals the mechanistic links between warming and plant community responses, and (ii) it provides quantitative metrics to assess vegetation dynamics and their impacts on CO
2 fluxes. This perspective therefore provides novel insights into how ecosystem structure and function respond to warming and reveals the underlying mechanisms involved.
2 Uncertainty in warming impacts on plant community
Long-term observations (
Boutin et al., 2017;
Myers-Smith et al., 2019), model simulations (
Botkin et al., 2007), and manipulative experiments (
Cowles et al., 2016;
Zhu et al., 2020) consistently show that climate warming drives shifts in plant communities worldwide. However, the impact of these warming-induced shifts on ecosystem CO
2 fluxes remains poorly understood. A major challenge lies in quantifying these community changes and linking them to ecosystem C cycling.
Numerous studies have attempted to quantify plant community dynamics by categorizing plants into functional types or life forms. However, this simplified approach often fails to capture the complexity of plant responses, leading to inconsistent results. For example, in Arctic tundra ecosystems, warming has been shown to favor shrubs and herbaceous plants (
Walker et al., 2006;
Myers-Smith et al., 2019), but no significant changes have been observed in these groups in northern wetlands (
Mäkiranta et al., 2018) and alpine meadows (
Price and Waser, 2000) under similar warming conditions. Moreover, even within the same functional group or life form, individual species often respond differently to warming. For instance, warming has been found to reduce moss abundance in Arctic regions (
Alatalo et al., 2020) and shrubs in peatlands (
Weltzin et al., 2003), yet some species within these groups have increased while others decreased. In Arctic tundra grasslands, the overall increase in grasses is driven by a few species, while others remained unaffected by warming (
Myers-Smith et al., 2019). A similar pattern emerges on the Qinghai-Xiazang Plateau, where warming decreases the abundance of forbs but has no effect on sedges, despite some species within both groups increasing (
Hu et al., 2021).
3 Plant species trait as mechanistic predictors of community responses to warming
The divergent responses suggest that the current framework, based on broad functional categories, is inadequate for predicting and understanding how plant communities respond to climate warming. However, plant traits offer a more unified approach to understanding of species’ complex responses to warming, transcending the limitations of taxonomic classifications (e.g., functional type, life form, photosynthetic pathway). For example, in temperature-limited ecosystems, warming has been shown to enhance vegetation biomass and height, intensifying aboveground light competition (
Hu et al., 2021). This shift confers a competitive advantage to taller species, resulting in the exclusion of shorter plants. Warming-induced soil drought can favor species with root traits conducive to efficient water acquisition, leading to an increase in grasses and a decline in sedges and forbs (
Ganjurjav et al., 2016;
Liu et al., 2018). However, some forb species, despite overall declines, have exhibited increased abundance due to traits such as underground storage organs, climbing growth habits, and parasitic strategies, which allow them to secure resources by extracting water and nutrients from neighboring plants (
Li et al., 2021). Moreover, a range of leaf traits, including leaf size, leaf nutrient content and specific leaf area, can also influence plant community responses to warming (
Bjorkman et al., 2020;
Zhu et al., 2020). Species with distinct traits exhibit specific responses to warming, leading to shifts in plant community composition. Studies have shown that plant communities are shifting toward more thermophilic compositions under warming, a trend observed at regional (
Boutin et al., 2017), national (
Martin et al., 2019), and continental scales (
Feeley et al., 2020).
These evidences suggest that plant species traits, as measurable characteristics reflecting plants’ long-term responses and adaptations to environmental changes, can offer a robust framework for elucidating how plant communities respond to warming and the underlying mechanisms. By linking observed patterns to these traits, researchers can gain deeper insights into vegetation responses across species, functional groups, and ecosystems. Identifying these thermophilic traits or trait combinations is crucial for understanding plant community responses to warming and predicting their future dynamics. However, current research remains limited, highlighting the need for further investigation in this area.
4 Community traits linking community shifts to ecosystem C fluxes
Growing evidence indicates that changes in plant community can significantly influence ecosystem C fluxes, often exceeding the effects of environmental factors (
Cahoon et al., 2012;
Ward et al., 2013 and 2015). However, substantial knowledge gaps remain in understanding how changes in plant communities influence the direction, magnitude, and climate sensitivity of ecosystem C fluxes, as well as the underlying mechanisms driving these processes. Extensive studies across diverse ecosystems and vegetation types have reported contrasting effects of warming-induced plant community shifts on ecosystem CO
2 fluxes. For instance, in US tallgrass and temperate prairies, changes in the C3/C4 ratio under warming significantly promoted soil CO
2 emissions (
Xu et al., 2015) and reduced soil C storage (
Pendall et al., 2011). Similarly, in the coastal wetlands of the Yellow River Delta, warming shifted the relative abundance of two dominant species, leading to decreased net ecosystem productivity (NEP) and ecosystem C sink (
Sun et al., 2021). Conversely, in the alpine meadows of the Qinghai-Xizang Plateau, warming increased grasses and forbs while reducing sedges, leading to higher NEP (
Peng et al., 2017). However, these studies often span various ecosystems, with various biotic and abiotic confounding effects. This heterogeneity makes it challenging to isolate the effects of plant community change and the underlying mechanisms (
D’Orangeville et al., 2016;
Kim et al., 2017;
Xu et al., 2020).
Few warming experiments have explored how changes in plant community composition influence C fluxes through targeted removal of specific functional groups. An early warming experiment incorporating functional group manipulations revealed that while warming enhanced NEP in shrub-dominated communities, it reduced NEP when herbaceous plants were present. These contrasting responses were attributed to differences in photosynthetic rates, resource allocation, litter chemistry, and soil microbial communities among functional groups (
Ward et al., 2013,
2015). Unlike plant manipulation experiments that randomly remove or combine plant functional types, warming-induced shifts in plant communities are usually directional. This key difference suggests that random species manipulation cannot properly reveal how warming-induced vegetation changes affect C cycling processes and its feedback to warming. Furthermore, as previously discussed, plant responses to warming can vary significantly both within and among functional groups, such as C3/C4 (
Cowles et al., 2016), shrubs/herbs (
Alatalo et al., 2020), or grasses/sedges/forbs (
Ganjurjav et al., 2016). It is not feasible to determine which plant functional groups or life forms should be removed in a way that reflects the complexity of warming-induced changes. Moreover, the directional shifts in plant community are shaped by trait-based environmental filtering. Under this warming filtering condition, plant communities tend to retain species with more similar and converging traits. The loss of functional complementarity under warming can reduce the community's capacity to buffer environmental fluctuations, potentially leading to greater variability in ecosystem C fluxes (
Chen et al., 2020;
Wolf et al., 2021). Such processes and mechanisms are difficult to capture through experiments involving random species removal or manipulation.
Plant community traits, derived from individual species traits and weighted by community composition, provide a crucial link between plant community structure and ecosystem processes. Species with different traits respond differently to climate change, driving shifts in community composition and structure (
Wang et al., 2017;
Xiao et al., 2021). These shifts, in turn, alter community-level traits, offering an effective way to quantify vegetation dynamics and their impacts on ecosystem CO
2 fluxes (
Gross et al., 2017;
Bjorkman et al., 2018). Studies have shown that community-level traits such as chlorophyll content, specific leaf area, and stomatal conductance can effectively explain variations in ecosystem CO
2 flux (
Wolz et al., 2017;
Durán et al., 2019). Furthermore, research has demonstrated that ecosystem CO
2 fluxes respond hierarchically to global change, with plant height playing a significant role in mediating these responses (
Liao et al., 2024;
Quan et al., 2024). These findings not only clarify complex community processes but also establish direct links between plant traits and ecosystem function.
5 The trait-based framework
In the face of climate change, growing attention has been paid to understanding how warming-driven shifts in plant communities influence ecosystem C cycling and associated C-climate feedbacks. A key challenge lies in predicting and quantifying warming-induced vegetation changes and linking them to ecosystem C dynamics. The trait-based approach offers a promising path forward by integrating these processes into a unified framework (Fig. 1). This framework links individual-level traits (e.g., specific leaf area, plant height, and leaf nitrogen content) to community-level properties using metrics such as the community-weighted mean and functional diversity. By integrating these metrics, the framework captures both the dominant trait within a community and the range of functional strategies present, which together govern C uptake and release. At its core, the trait-based framework seeks to identify the key traits or trait combinations that mediate plant community responses to warming and regulate ecosystem CO2 fluxes. These insights provide a theoretical basis for incorporating trait indicators into ecosystem models, thereby enhancing the accuracy of ecosystem C flux simulations and improving projections of ecosystem responses under future climate scenarios.
A recent study that combined a field warming experiment with a regional transect investigation on the high-elevation Qinghai-Xizang Plateau provided a trait-based perspective on how plant communities respond to warming and regulate ecosystem C fluxes in cold and high-altitude region. This study suggested that warming promoted plant growth and intensified aboveground competition for light, favoring taller species. Warming not only increased the height of plant species but also raised the proportion of taller species, collectively promoting the overall height of the plant community. These changes enhanced NEP, its temperature sensitivity and soil C storage (
Quan et al., 2024). As a key trait in the cold and high-elevation biomes, plant height plays a central role in mediating both plant community composition and ecosystem C sequestration under warming (Fig. 2). This trait-based linkage of climate warming, plant community structure and traits, and ecosystem CO
2 fluxes, offers a novel perspective for predicting the direction, magnitude, and sensitivity of ecosystem C fluxes in a warming world.
However, despite the vast number of studies on climate warming, C fluxes and plant traits individually (Fig. 3), only about 4% to 10% of these publications involve cross-disciplinary research, and just 283 (0.03%) papers have explicitly used plant traits to understand the effects of global warming on C fluxes. Given the demonstrated effectiveness of plant traits in explaining how plants and communities respond to warming and regulate ecosystem C dynamics (
He et al., 2019;
Quan et al., 2024), such integrative research remains significantly underdeveloped. Nonetheless, it is worth affirming that over the past decade, an increasing number of studies have begun to employ plant traits as a bridge liking climate warming and C fluxes (Fig. 3). This suggests that trait-based approaches will become more prevalent in future investigations of global change impact of global warming on the C cycle.
6 Improving ecosystem models with community traits
Ecosystems models commonly classify vegetation into PFTs, such as C
3 and C
4 plants, to assign photosynthetic and water-use efficiency parameters based on flux data (
Kowalczyk et al., 2006;
Mauritsen et al., 2019;
Danabasoglu et al., 2020). While this classification has facilitated global modeling of carbon and water fluxes, evidence from trait-based studies indicates that PFTs often fail to capture the full spectrum of trait diversity within plant communities. Specifically, they may underestimate average trait values or fail to reflect the broad variability observed
in situ (
Kattge et al., 2009;
Van Bodegom et al., 2012). Hence, models need to use trait data to parameterize models instead of relying solely on PFTs.
And indeed, some processes in models are represented using plant traits, like the C and nitrogen (C:N) ratio, which could affect plant photosynthesis and respirations (
Kowalczyk et al., 2006;
Danabasoglu et al., 2020;
Wang et al., 2021,
2022b). However, many models still rely on trait data from a limited number of species or use simple arithmetic means, which poorly represent the functional diversity and structure of entire plant communities. Hence, incorporating community-level traits information, such as community-weighted means and functional diversity, can improve the ecological realism and predictive accuracy of these models.
In addition, advances in trait-based research are paving the way for a new generation of ecosystem models that incorporate a broader range of vegetation traits (
He et al., 2019). Increasingly, researchers recognize that incorporating more trait parameters is an effective measure to enhances model performance (
Larson and Funk, 2016;
Lu et al., 2017;
Wang et al., 2022a). As trait databases continue to expand, future models will likely integrate more community-level traits, thereby improving the accuracy of carbon cycle simulations under changing climate conditions.
7 Conclusions
Climate warming profoundly affects plant communities and ecosystem C dynamics, presenting both a critical research challenge and policy concern. Plant traits offer a powerful, mechanistic framework for linking community composition changes to ecosystem C fluxes under warming, offering valuable insights into these intricate interactions. Future research should focus on integrating trait-based framework with long-term experimental observations and ecosystem modeling to improve predictions of C cycling across diverse ecosystems. Identifying key traits that govern plant responses to warming, particularly those influencing growth, competition, and resource acquisition, will enhance our ability to predict ecosystem productivity and carbon sequestration under future climate scenarios. Furthermore, incorporating community-level traits into ecological models, alongside traditional plant functional types, will improve the accuracy and sensitivity of C flux projections.