Biological invasion is a global problem that poses a threat to local plant communities, alters the patterns of macrobenthic animals, affects the habitat and food sources of migratory birds, and has negative effects on material circulation, energy flow, socio-economic activities, and other aspects of coastal wetland ecosystems (Sampaio et al., 2021; Zhang et al., 2021a; Li et al., 2022; He et al., 2023). Most invasive species can survive in large geographic areas where they germinate, colonize, grow, reproduce, expand, and develop corresponding adaptation strategies across latitudes (Liu et al., 2017 and 2022; Chen et al., 2023). Latitudinal gradients in abiotic factors, including temperature, precipitation, and soil physicochemical properties, increase environmental heterogeneity, shape the plant traits of invasive species, and form latitudinal patterns of plant communities coexisting with local and invasive species (Kirwan et al., 2009; Liu et al., 2020; Cheng et al., 2022). Altered plant traits (including plant height, stem diameter, leaf traits, specific leaf area, dry matter content, shoot density, productivity, reproductive traits, ecostoichiometry, etc.) through phenotypic plasticity promote the probability of successful invasion by invasive species, recognized as important mechanisms for invasion (Maron et al., 2004; Kirwan et al., 2009; Liu et al., 2017; Liu et al., 2020; Liu et al., 2020; Zhang et al., 2021a; Chen et al., 2022; Cheng et al., 2022; Liu et al., 2022; Zheng et al., 2022). In recent decades, research on plant traits has made good progress, and the introduction of new technologies, represented by stable isotopes, has provided new methods and ideas for exploring the mechanisms of invasive species (Hill et al., 2018; Watson et al., 2018; Wang et al., 2023). Latitudinal patterns of isotope signatures in invasive plants across coastal wetlands have become a new topic.

Stable isotopes, a type of natural isotopes existing in organic organisms, are non-radioactive and stable (Lin and da SL Sternberg, 1993; Feng et al., 2018; Chen et al., 2023). They typically possess a relatively long half-life and are not limited by their duration. Stable isotopes offer numerous advantages, including easy operation, high sensitivity, safety, non-toxicity, rapid detection, accurate results, and relative stability (Spivak and Reeve, 2015). They primarily exploit the same physiological and biochemical properties of labeled compounds and their corresponding non-labeled compounds to trace the intricate and variable chemical reactions and biological processes in organic organisms. This facilitates the observation of metabolic patterns and bioavailability of the tracked substance in the organism by monitoring changes in isotopic ratios (Bai et al., 2012; Kou et al., 2020; Xia et al., 2023a). Carbon (C), nitrogen (N), and sulfur (S) are essential components in plant tissues, and their corresponding stable isotopes are closely associated with plant physiological metabolism, growth, and development processes (Hill et al., 2018; Liu et al., 2021; Wittyngham et al., 2023; Xiong et al., 2023). Plant photosynthesis plays a crucial role in the fractionation effect of δ ¹³C. The δ ¹³C can be utilized to study the chemical development process of biogeography, the allocation of photosynthetic carbon in plants, the identification of plant photosynthetic pathways, and the evaluation of water use efficiency and biomass changes in plants characterizing the litter decomposition process (Liu et al., 2018; Zhang et al., 2021a; Xia et al., 2023b). The δ ¹⁵N isotope is commonly employed to assess the utilization efficiency, loss, nutrient uptake, and transport process of nitrogen elements in plant organisms and even plant communities (Hill et al., 2018; Xia et al., 2023a). The δ ³⁴S isotope in plants can provide crucial information on the absorption of atmospheric sulfides by plants and the metabolism of sulfur in plants, offering a powerful tool for a deeper understanding of the interaction between organisms and their living environment (Guo et al., 2020; Jinks et al., 2020; Guiry et al., 2022). Stable isotopes, especially their local and global patterns, play a significant indicative role in monitoring short-term and long-term environmental changes in the biosphere. Applying stable isotopes in the study of invasive plant species in coastal wetlands and understanding the information reflected by isotopic changes contribute greatly to revealing the invasion mechanism.

Spartina alterniflora, recognized as a typical invasive plant, is a perennial monocotyledonous plant belonging to the Poaceae family (Cheng et al., 2022; Jia et al., 2022). It possesses extensive roots and robust reproductive capabilities, commonly growing in the intertidal zones of estuaries, bays, coastal mudflats, and tidal-influenced beaches worldwide (Humphreys et al., 2021; Mao et al., 2023). S. alterniflora plays a significant role in ecological and economic benefits, including carbon and nitrogen fixation, wind and wave prevention, embankment and beach protection, soil improvement, and the expansion of animal and plant habitats (Lu et al., 2020; Meng et al., 2020). However, the negative ecological impact of S. alterniflora invasion is becoming increasingly severe, affecting the structure and composition of biological communities. This invasion damages the composition and transmission of the food chain in coastal wetland ecosystems, leading to extreme instability in the ecological environment of coastal wetlands (Jinks et al., 2020; Li et al., 2022; Jia et al., 2022). Due to its high tolerance to salinity, rapid growth rate, and extensive range, S. alterniflora alters surrounding environmental factors by secreting a significant amount of salt into the environment during high-intensity transpiration. Simultaneously, it is an invasive species well-adapted to the coastal wetland environment, suppressing the growth of local plants in the surrounding environment by seizing living space and resources, thereby changing the structure and function of wetlands (Liu et al., 2017; Mao et al., 2019; Liu et al., 2022; Liu et al., 2020; Humphreys et al., 2021). Previous studies on S. alterniflora have focused on the invasion mechanism, physiological responses under different driving forces, competition mechanisms between native and invasive species, ecological prevention and control measures, and comprehensive analysis and utilization of biomass energy (Courtney et al., 2016; Ma et al., 2019; Hessini et al., 2022; Li et al., 2022). Some studies have explored S. alterniflora stable isotopes, systematically analyzing element dynamics during the decomposition process of S. alterniflora residues and changes in plant-soil element pools and nutrient transport processes. He et al. (2023) compared the trophic contribution of S. alterniflora to the macrozoobenthos between the dense S. alterniflora area and adjacent tidal bare mudflat in the Hepu coast by analyzing δ ¹³C and δ ¹⁵N. Wang et al. (2024) found that S. alterniflora invasion increased the values of δ ¹³C and δ ¹⁵N, as well as organic matter decomposition. Wu et al. (2024) used a ¹⁵N stable isotope dilution technique to investigate sediment gross N mineralization and NH₄ ⁺ immobilization under aerobic and anaerobic conditions in S. alternifora communities. However, there has been little attention to the distribution pattern and influencing factors of δ ¹³C, δ ¹⁵N, and δ ³⁴S in S. alterniflora across latitudes (Kinney and Valiela, 2018; Chen et al., 2021; Zhang et al., 2021 and Zhang et al., 2021). Additionally, there is minimal research on the impact of the life-death status of S. alterniflora on isotopic distribution.

Here, we compared the latitudinal patterns of the isotope signatures (δ ¹³C, δ ¹⁵N, δ ³⁴S) of S. alterniflora and their responses to climate drivers under different plant life-death status by collecting isotopic data from literature records at 267 sites across coastal wetlands. Building upon previous findings on plant traits of S. alterniflora, we tried to address the following questions: (1) Do the latitudinal patterns of the isotope signatures of S. alterniflora vary with life-death status? (2) How is the geographical variation in S. alterniflora isotope signature influenced by mean annual temperature (MAT) and mean annual precipitation (MAP)? (3) Have strong coupling relationships formed between the isotope signatures of S. alterniflora? We hypothesized that: (1) The latitudinal patterns of the S. alterniflora isotope signature under the life status would outperform the dead status; (2) Geographical variation in S. alterniflora isotope signature would be driven by MAT and MAP; (3) The δ ¹⁵N and δ ³⁴S of S. alterniflora would respond to the corresponding δ ¹³C in a linear or nonlinear form.

We observed a consistent pattern in the δ ¹³C, δ ¹⁵N, and δ ³⁴S values of S. alterniflora across latitudes, providing evidence for the latitudinal variation in vegetative growth traits. These traits are likely associated with the plant’s invasive mechanisms. Previous studies have documented general patterns, such as linear or binomial, in plant height, stem diameter, leaf characteristics (leaf area, thickness, toughness, specific leaf area, dry matter content), shoot density, plant productivity, reproductive traits (seed set, seed production, seeding density, seed germination, first flower day, flowering culm, number of spikelets), ecostoichiometry (C, N, P, and their ratios), and leaf litter decomposition rate in response to increasing latitudes within the specified range (Kirwan et al., 2009; Liu et al., 2017; Liu et al., 2020; Liu et al., 2020; Chen et al., 2022; Cheng et al., 2022; Liu et al., 2022; Zhang et al., 2021a; Zheng et al., 2022). The latitudinal patterns of vegetative traits collectively regulate the growth, reproduction, and expansion of S. alterniflora through plastic deformation strategies. The plastic deformation strategies altered plant form and function so as to match environmental changes in a new environment, these enhancing plants competitiveness for space and resources, allowing it to occupy vacant ecological niches (Liu et al., 2017; Chen et al., 2023; Xiong et al., 2023). Previous research has shown that the plant height of S. alterniflora forms a convex curve with increasing latitudes (20°N~40°N), aligning with the latitudinal pattern of δ ¹³C but contrasting with that of δ ¹⁵N in S. alterniflora (Liu et al., 2017). In general, larger S. alterniflora plants with greater height exhibit strong photosynthesis, altering carbon isotope fractionation and increasing the potential accumulation of ¹³C (Lin and da SL Sternberg, 1993; Essemine et al., 2020; Mao et al., 2023). When nutrient resources are limited, larger plants typically require a significant amount of nutrients to sustain rapid growth, resulting in a dilution of ¹⁵N and a decrease in its accumulation within the plant (Hill et al., 2018; Chen et al., 2022). Moreover, an increase in dry matter content induces plant senescence, leading to a reduction in ¹⁵N-related enzymes and influencing plant ¹⁵N levels (Hessini, 2022; Xia et al., 2023a). Hence, the varied latitudinal patterns of S. alterniflora’s plant traits facilitate its adaptive response to environmental changes associated with different latitudes.

Plant life-death status have complex effects on isotopes, and then affecting their latitudinal patterns. In this study, the plant life status did not alter the δ ¹³C and δ ³⁴S values or their corresponding latitudinal patterns in S. alterniflora. These findings are consistent with prior research; Schwamborn et al. (2002) and Kieckbusch et al. (2004) discovered that live leaves and senescent leaves exhibited similar δ ¹³C values. Similar evidence was observed in the δ ¹³C of Kandelia candel and Rhiziophora mangle during the senescence process (Wooller et al., 2003b). However, Rao et al. (1994) reported no difference in δ ¹³C between fresh and senescent tissues of five mangrove species in Kenya, while the other four mangrove species displayed differentiation. Robin et al. (2024) found that fresh leaves are more enriched in ¹³C than senescent leaves for Avicennia marina and Rhizophora stylosa, but for R. stylosa they are less enriched in ¹⁵N. Furthermore, we observed that the death of plants led to a reduction in δ ¹⁵N in S. alterniflora compared to their living status. This phenomenon may be attributed to the inactivation of N-related enzymes in S. alterniflora (Hessini, 2022; Xia et al., 2023a). The status of plant death resulted in a δ ¹⁵N response in the form of a concave curve with increasing latitude but exhibited a less distinct response under the plant life status. These findings suggest that live S. alterniflora demonstrates a broad range of δ ¹⁵N responses to latitude, particularly at higher latitudes. There is no consensus on whether there are differences in plant isotopes and their latitudinal patterns across species under different life states. This inconsistency with our hypothesis (1) leads us to speculate that variations in plant isotopes and their latitudinal patterns under different life status may depend on the species, its strength, the type of isotopes (Wooller et al., 2003b; Rao et al., 1994), and specific evidence that needs further exploration.

MAT and MAP play crucial roles in shaping latitude and influencing plant growth and reproduction (Yuan and Chen, 2009; Zhang et al., 2019; Xia et al., 2023a). Prior studies have demonstrated that temperature and precipitation contribute to the formation of linear or quadratic polynomial patterns in plant growth and reproductive traits (Kirwan et al., 2009; Liu et al., 2017, Liu et al., 2020; Liu et al., 2020; Liu et al., 2022; Chen et al., 2022; Cheng et al., 2022; Zheng et al., 2022). Latitude changes increase environmental heterogeneity, especially in hydrothermal environments; Simultaneously, it shapes different plant traits to adapt to environmental changes. Therefore, we hypothesize that the isotopes of S. alterniflora, closely linked to these traits, are affected by MAT and MAP. While general patterns of δ ¹³C, δ ¹⁵N, and δ ³⁴S in response to MAT along latitudinal gradients were identified, this was not observed for MAP, which is not entirely consistent with our hypothesis (2). A consensus emerges, indicating that MAT is the controlling factor for the latitudinal patterns of δ ¹³C, δ ¹⁵N, and δ ³⁴S in S. alterniflora. The marginal influence of precipitation in this study warrants thorough consideration, deviating from previous research conclusions (Yuan and Chen, 2009; Xia et al., 2023a). In Supplementary Figure S2 , MAP exhibits a trend of decreasing and then increasing with latitude. Additionally, MAP is influenced by various factors, including the relative position of land and sea, terrain, pressure bands, wind belts, monsoons, cyclones, fronts, underlying surfaces, ocean currents, and human activities (Fick & Hijmans, 2017). The complexity of these factors reduces the interpretability of latitude’s impact on MAP and disrupts the response patterns of δ ¹³C, δ ¹⁵N, and δ ³⁴S in S. alterniflora to MAP. Interestingly, the δ ¹⁵N of S. alterniflora under live plant conditions shows a significant response to MAT, unlike its death status. This observation aligns with the notion that temperature influences enzyme activity in live plant bodies (Hessini, 2022). The δ ¹³C and δ ³⁴S of live S. alterniflora exhibit a significant response to MAP due to their stability and the importance of precipitation for plant survival (Yuan and Chen, 2009; Xia et al., 2023a). Phenotypic plasticity, by altering plant isotopes and their other traits, fully ensures their survival in changing environments, and enables invasive plants to successfully customize and spread in the invasive ranges.

The relationships among plant elements or isotopes are crucial for studying plant adaptation mechanisms at the single-species scale and element flux in food webs at the whole ecosystem scale (Gao et al., 2018; Jinks et al., 2020; Li et al., 2022). However, the paired relationships between any two indicators of δ ¹³C, δ ¹⁵N, and δ ³⁴S in S. alterniflora have been overlooked. In this study, we hypothesize that the δ ¹⁵N and δ ³⁴S of S. alterniflora exhibit stable relationships with the corresponding δ ¹³C. The δ ¹⁵N of S. alterniflora decreases with increasing δ ¹³C, supporting parts of hypothesis (3). When having similar δ ¹³C values, the decrease in δ ¹⁵N of deceased S. alterniflora disrupts the general relationship between δ ¹³C and δ ¹⁵N. Additionally, the indistinct relationships between δ ³⁴S and δ ¹³C (or δ ¹⁵N) of S. alterniflora may be associated with the δ ³⁴S in the environment. Excessive δ ³⁴S in the soil (found in salt marshes with sulfate-type soil) or atmosphere (in areas with acid rain) leads to an increase in δ ³⁴S in plant bodies, resulting in a mismatch in the relationship between δ ³⁴S and δ ¹³C (or δ ¹⁵N) of S. alterniflora (Guo et al., 2020; Jinks et al., 2020; Guiry et al., 2022). These findings highlight the isotopic flexibility within S. alterniflora.

Although our results provide strong evidence for the latitudinal patterns and their climate drivers of the δ ¹³C, δ ¹⁵N, δ ³⁴S isotope signatures of S. alterniflora across plant life-death status based on a global analysis, there were several limitations in this study, such as how soil isotope signatures affected plant isotope signatures. Soil is recognized as a key factor influencing available nutrient for plant, and their large-scale patterns of isotope signatures have an imprint on plant isotope signatures (Amundson et al., 2003; Craine et al., 2015). Plant δ ¹³C (δ ¹⁵N) was significantly positively related to soil δ ¹³C (δ ¹⁵N) across varied plant species and functional types (Peri et al., 2012; Xia et al., 2023b). Although soil δ ¹³C and δ ¹⁵N was shaped by MAT and MAP, future research should pay attentions to the imprint of soil isotope signatures on corresponding isotope signatures.

The latitudinal patterns of δ ¹³C, δ ¹⁵N, and δ ³⁴S in S. alterniflora are depicted as a convex curve, a concave curve, and an increasing straight line, respectively. The responses of δ ¹³C, δ ¹⁵N, and δ ³⁴S in S. alterniflora to MAT manifest as a decreasing line, a concave curve, and a decreasing line, respectively, but exhibit indistinct responses to MAP. The life-death status of plants alters the δ ¹⁵N-latitudinal patterns and their responses of δ ¹³C, δ ¹⁵N, and δ ³⁴S in S. alterniflora to MAT. The δ ¹³C and δ ³⁴S of living S. alterniflora demonstrate robust responses to MAP. Plant death status results in a significant decrease in δ ¹⁵N, but not in δ ¹³C and δ ³⁴S. Paired δ ¹⁵N and δ ¹³C of S. alterniflora exhibit a noteworthy negative relationship across the entire dataset and plant life status. All these findings provide evidence of robust ecological plasticity and adaptability across geographic clines.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

DZ: Writing – original draft, Writing – review & editing. HW: Data curation, Investigation, Visualization, Writing – original draft. XL: Data curation, Investigation, Writing – original draft. KA: Data curation, Writing – original draft. WH: Writing – review & editing. TW: Data curation, Investigation, Writing – original draft. MZ: Writing – original draft, Writing – review & editing. ST: Conceptualization, Writing – review & editing.