Trait variability in a widespread and dominant salt marsh grass in a South Carolina estuary

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Even within a single species, trait expression can vary across environmental gradients such as elevation and salinity. However, while variation in plant height has been relatively well documented in species such as Spartina alterniflora (also known as Sporobolus alterniflorus; smooth cordgrass ) , exploring the extent and patterns of other trait expression across natural environmental gradients provides insight into how multiple environmental drivers shape plant form and function. This study examined trait variability in S. alterniflora , a dominant salt marsh grass along the Atlantic coast of the United States. Plants were surveyed across an elevation gradient along three transects at two sites within the North Inlet–Winyah Bay National Estuarine Research Reserve, South Carolina. Here, we document phenotypic traits (plant height, panicle number and length, and foliar nutrients) and identify those traits that vary across elevation and salinity gradients. Plant height declined with elevation (195 cm/m at site A; 180 cm/m at site B) but showed inconsistent relationships with salinity. Panicle number decreased by 1.1 per PSU in some transects, and panicle length declined with elevation (19.8 cm/m at site A; 16.0 cm/m at site B). Foliar carbon and nitrogen showed no significant trends. These findings improve our understanding of how S. alterniflora phenotypic traits vary relative to marsh elevation and salinity, providing insight into the potential resilience and adaptive capacity of a salt marsh foundation species under changing environmental conditions. Spartina phenotypic traits salt marsh salinity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Salt marshes are highly productive coastal ecosystems that provide essential ecological functions such as carbon sequestration, shoreline stabilization, and habitat provisioning, and support valuable services including tourism and commercial fisheries (Barbier et al., 2011 ; Purcell et al., 2020 ). Salt marsh plant communities experience a range of environmental conditions and disturbances due to tidal flooding, salt deposition, upland runoff and storms. The plant communities in these environments are adapted to growing in these harsh conditions as reflected in morphological differences along environmental gradients found in salt marshes (Pennings & Bertness, 2001 ). One of the defining features of coastal salt marsh ecosystems is the elevation gradient, which has been well-documented in terms of its effects on inundation, salinity, and plant zonation (Pennings & Bertness, 2001 ). Across this gradient, plant productivity has been shown to increase from low to high elevations (Morris et al., 2002 ) while plant species distribution can be limited by both salinity and interspecific competition across the gradient (Pennings et al., 2005 ). Along the Atlantic and Gulf coasts in the southeastern United States, Spartina alterniflora is a dominant C4 grass species adapted to saline and anoxic conditions across the salt marsh elevation gradient. S. alterniflora is native to the U.S. Atlantic coast but considered invasive in salt marshes in other regions (Ayres et al., 1999 ; Normile, 2004 ). The root and rhizome structures of S. alterniflora help stabilize soils during storm and high tide events (Cahoon et al., 2021 ) and, as such, are an integral part of coastal ecosystems that provides habitat for a diverse and productive community of salt marsh-affiliated species (Minello & Webb, 1997 ; Minello et al., 2012 ), which can also vary across the marsh platform elevation gradient (Dunn et al., 2023 ). Southeastern coastal ecosystems are experiencing stressors from press and pulse disturbances (IPCC, 2023; Harris et al., 2018) which can impact salt marsh vegetation in multiple ways. In the case of S. alterniflora marshes, increased inundation time from sea level rise over a 10-year period resulted in a 0.94% reduction of belowground biomass (Runion et al., 2025 ). Warming winter soils are a main driver for earlier S. alterniflora green-up times (O’Connell et al., 2020 ) and warming air temperatures can shift plants towards more clonal reproduction and less sexual reproduction (Jiang et al., 2025 ). Extreme hurricane-related pulse events resulted in mass S. alterniflora dieback due to flooding and extreme precipitation (Stagg et al., 2021 ). Salt marsh vegetation can help mitigate erosional losses from sea level rise and more frequent storm events through soil accretion by adding organic matter and helping retain mineral soil (Morris et al., 2002 ; Cahoon et al., 2006 ). Nevertheless, their functional role in the ecosystem assumes their own ability to persist through changing conditions. Marsh vegetation productivity may increase with rising mean annual temperatures, potentially offsetting erosional losses (and associated vegetation) from sea-level rise in some locations (Kirwan et al., 2009 ). However, marshes' elevation gains through soil accretion are predicted to lag behind the pace of sea-level rise (Crosby et al., 2016 ), a trend that could be exacerbated or ameliorated by further human impacts (Kirwan & Megonigal, 2013 ). The fate of these marshes will partially depend upon the resiliency and adaptability of the plant species that live there, particularly dominant species such as S. alterniflora . Plant trait variation is an important quality that reflects adaptation and potential resilience to abiotic drivers. For example, S. alterniflora grows in short form and tall form, differing in plant height along the marsh platform. Tall form plants grow near creek edges where elevation is lower and inundation by the tide is more frequent. Short form plants grow at higher elevations but also occur in heterogeneous patches across the salt marsh platform. S. alterniflora exhibits these different growth forms based on marsh location (intertidal zone vs. panne; Shea et al., 1975 ) and nutrient supply (Valiela et al., 1978 ), with both factors potentially influencing growth form simultaneously. Further evidence attributes the distribution of different growth forms to plant macronutrient concentrations (Ornes & Kaplan, 1989 ) and salinity (Pennings & Bertness, 2001 ). Lin et al. ( 2019 ) examined rhizosphere bacterial community composition in the field and in a common garden, supporting studies like Valiela et al. ( 2023 ), which show that nitrogen abundance promotes the tall form. Although abiotic factors are correlated with S. alterniflora height, studies like Gallagher et al. ( 1988 ), Seliskar et al. ( 2002 ), and Zerebecki et al. (2021) show persistent trait expression amid transplantation, confirming that height is a result of both environmental and genetic factors (Anderson & Treshow, 1980 ), as well as epigenetic factors (Mounger et al., 2022). Many studies of S. alterniflora have focused on variation in plant height across the marsh platform, but other morphological and fitness-related traits may also be important for understanding how this species may respond to current and predicted environmental changes (IPCC, 2023). In particular, the relationship between growth form (tall vs. short) and reproductive traits, such as panicle length and number, remains unclear. For example, inflorescence length, which is correlated with flowering stem height (Crosby et al., 2015 ), may differ between growth forms and across the marsh platform. However, environmental stressors such as salinity and flooding, more intense at lower elevations near creek edges, may suppress reproductive output, potentially obscuring trait relationships. For example, panicle number, an indicator of plant health in other Poaceae species, decreases under salt stress (Razzaq et al., 2020). If this holds for S. alterniflora , we expect panicle number to be lower under salinity stress, such as at creek edges, even though larger plant size in these areas might otherwise suggest greater reproductive output. In addition to reproductive traits, physiological indicators of stress, such as foliar C:N, which may reflect reduced nitrogen uptake under salinity stress (Bradley & Morris, 1991 ), could also decrease across the marsh platform and provide further insight into how S. alterniflora responds to environmental gradients. This study investigates how panicle number, panicle length, plant height and foliar nutrient concentrations vary along salt marsh platforms in local S. alterniflora populations. This study tested the hypothesis that elevation and salinity gradients across the marsh platform drive corresponding variations in S. alterniflora phenotypic traits, with plants at the lower elevation (higher salinity) exhibiting lower reproductive output including shorter height, shorter and fewer panicles, and higher C:N relative to those in higher elevations (lower salinity). To test this hypothesis, plant height, panicle length and number, and foliar nutrient concentrations were measured across the marsh platform at two salt marsh sites in coastal South Carolina. Materials and Methods Site description, elevation and porewater salinity This study examined variation in S. alterniflora traits within a representative back-barrier salt marsh in the North Inlet-Winyah Bay National Estuarine Research Reserve in Georgetown, SC, USA (Fig. 1 a). The North Inlet estuary is an ocean-dominated system with long-term mean salinities in tidal creeks > 30 psu. Freshwater input into this estuary is via shallow groundwater and surface flows from the surrounding watershed during precipitation events. We collected data from 2 distinct sites within a contiguous salt marsh along Crabhaul Creek, an intertidal creek on the western edge of the North Inlet estuary. Our study sites are approximately 2 km apart; each site includes 3 replicate transects (~ 210 m long at Site A, ~ 75 m long Site B) running from the creek bank to the upland forest edge. Within each of these 6 transects, data on plant traits and marsh biogeochemical conditions were collected from permanently established plots where S. alterniflora was present along the elevation gradient. The number of permanent plots containing S. alterniflora was 4 for Site A and 6 for Site B. Permanent plots were grouped into upper-elevation and lower-elevation marsh zones using a k-means clustering (k = 2) on elevation (m; NAVD88) and distance to the forest edge (m). Clustering was run separately for each site. Prior to clustering, both variables were z-standardized to equalize scale. While these two sites are both S. alterniflora -dominated salt marshes with similar tidal inundation frequencies (low marsh plots inundated > 40% of the time across both sites; Krask et al., 2022 ), they differ in ways that could play a role in plant phenotypic expression. Namely, Site B has a steeper slope due to the narrower marsh platform; Site B is also exhibiting a more uniform reduction in porewater salinity through time while salinity changes are patchier at Site A (Krask et al., 2022 ). Both sites are experiencing long-term increases in inundation, with plots adjacent to the creekbank showing the highest rates of change in inundation time (Krask et al., 2022 ). Orthometric height (elevation, in m) of each plot was measured in 2021 with a Trimble R8s real-time kinematic global positioning system (RTK-GPS) and referenced to the North American Vertical Datum of 1988 (NAVD 88). Plot-level elevation values used here are calculated from triplicate measurements made in opposite corners and within the center of each plot in the field. Sediment porewater salinity at each plot was measured in May and June 2023. Specifically, porewater samples were collected in triplicate from each plot during each month at a sampling depth of 25 cm. Porewater was collected using modified diffusion equilibrators, which were 20mL glass scintillation vials filled with deionized water and covered with nitex mesh (20 µm) membranes secured with an open-topped screw cap. Vials were housed inside porous PVC pipes embedded into the marsh sediment, and vials were left to equilibrate for approximately one month. Upon retrieval, vials were capped and returned to the lab on ice and processed immediately. Salinity was measured with a handheld Mettler-Toledo Seven2Go pro conductivity/salinity probe, and replicate samples were averaged to generate plot-level mean values. Phenotypic traits Along each of the six transects, vegetation measurements were repeated within each 1-m 2 permanent plot in the first week of September 2023. Plant height was identified as non-destructive measurements of the season’s growth success. Plant height was measured for four randomly selected flowering plants within each permanent plot. The total number of S. alterniflora panicles were counted within each permanent plot where S. alterniflora was present (Fig. 1 a). Panicle length was determined as the mean of four randomly selected panicles measured within each permanent plot. Leaf nutrient concentration was measured from leaves collected during the same period. Five randomly selected leaf samples were collected from individual plants in each permanent plot. Leaves were dried at 60 ºC for 48 hours, ground with a Wiley mill and analyzed for carbon and nitrogen content using a LECO elemental analysis instrument (LECO Corporation, USA). Statistical analyses Within each site, upper- and lower-zone observations were compared using the Wilcoxon rank-sum (Mann–Whitney) test (two-sided) (Mann & Whitney, 1947 ). Dose‒response curves (Poorter et al., 2010 ; Poorter et al., 2012 ) were constructed to analyze the salinity variations with elevation at each site and the responses of plant height, panicle number, panicle length, and foliar nutrients (CN ratio, carbon content, and nitrogen content) to elevation and salinity changes. Here, local regression (loess), a nonparametric method, was employed to fit the dose‒response curve. Linear regressions were used to assess the trends of these parameters in response to elevation and salinity. Statistical significance of the trends (regression slopes) was evaluated at the α = 0.05 probability level using Student’s t test. All the analyses were performed using Python 3.11.6 ( https://docs.python.org/release/3.11.6/ ). Results Elevation and porewater salinity The transects at sites A and B exhibited similar elevation ranges despite their varying distances from the forest edge to the creek bank (Fig. 1 b). Specifically, plots with S. alterniflora at site A spanned 126 to 267 m from the forest edge, covering elevations from − 0.140 to 0.514 m. In contrast, plots with S. alterniflora in site B were closer to the forest edge, ranging from 10 to 78 m away, and covered elevations between 0.028 and 0.524 m. The upper-elevation S. alterniflora zones identified by k-means clustering within sites A (0.37 ± 0.12 m) and B (0.39 ± 0.07 m) had similar mean elevations, but the lower-elevation zone in site A (0.03 ± 0.08 m) was significantly lower than that in site B (0.17 ± 0.08 m; Fig. 2 a, b). Sediment porewater salinity did not significantly differ between the upper and lower S. alterniflora zones across the two sites (Fig. 2 c-f). In the low-elevation plots closest to the creek bank, the mean porewater salinities were slightly greater (by 0.2–0.6 psu) than those in the upper-elevation plots, except for site A in June. Furthermore, no significant trends in porewater salinity correlated with increasing elevation except for site A in June (Fig. 2 h). Notably, a linear increase in porewater salinity with elevation was observed for site A in June, at a rate of 5.7 psu per meter (p = 0.007, n = 11) (Fig. 2 h). The porewater salinities in both sites were greater in June than in May (p = 0.006), with increases of 2.7 psu in Site A and 1.3 psu in Site B mean salinity values. Phenotypic traits We observed a marked difference in plant height across the different marsh zones. Specifically, there was a 44% reduction in plant height transitioning from the lower- to upper-elevation S. alterniflora zone in Site A (p = 0.06 ) and a 37% reduction in Site B (p = 0.0002) (Fig. 3 a, b). Additionally, we found significant linear decreases in plant height with increasing elevation in both sites, with values of − 195 cm per meter of elevation gain in Site A and − 180 cm per meter in Site B (Fig. 3 c, d). The decreasing trends suggested a strong correlation between elevation and plant height, particularly at relatively lower elevations (i.e., < 0.35 m; Fig. 3 d). We also found that when the salinity exceeded 18 psu plant height was lower as seen in site A (Fig. 3 e). Total panicle numbers did not differ between marsh zones in either site (Fig. 4 a, b). The fluctuations in panicle numbers in Site B appeared more acutely responsive to variations in salinity than did those in Site A (Fig. 4 e, f), with a significant reduction of 1.1 panicles per unit increase in salinity (p = 0.043, n = 18). Panicle length exhibited patterns similar to those of plant height in response to variations in elevation and porewater salinity. Panicle length did not vary between lower and upper S. alterniflora zones at site A (Fig. 5 a) but there was a significant decrease of nearly 25% in site B (p = 0.002) (Fig. 5 b). We also found linear decreases in panicle length with increasing elevation for both sites, with decreasing values of − 19.8 cm per meter (p = 0.020, n = 11) (site A; Fig. 5 c) and − 16.0 cm per meter (p = 0.001, n = 18) (site B; Fig. 5 d). Panicle length also decreased across the salinity gradient at site A (p = 0.002, n = 11) (Fig. 5 e). Foliar nutrients Our investigation revealed no relationship between foliar carbon-to-nitrogen (C:N) ratios with elevation (Fig. 6 ). Site B exhibited a negative relationship between C:N and salinity (p = 0.027, n = 18) (Fig. 6 f). There were no differences between foliar carbon, or nitrogen concentrations between the lower and upper zones (Fig. 7 ). Discussion Based on replicated sampling during the growing season, we find that S. alterniflora exhibits distinct variation in some demographic traits across both elevation and porewater salinity gradients within a representative salt marsh in the southeast United States. Importantly, other traits did not respond to changes in elevation or porewater salinity. Salt marsh sites A and B within the North Inlet-Winyah Bay NERR showed similarities in elevation ranges despite differences in their distances from the forest edge to the creek bank, demonstrating that local topography likely plays a significant role in shaping the elevation profiles of these sites. The transect along Site A was longer but with a similar elevation gain to site B. The significant difference in lower-elevation zones between site A and site B may indicate variations in tidal influence, which is further supported by the trend observed at site A, where higher elevations were associated with increased porewater salinity in June. The increase in porewater salinity observed in June compared to May across both sites likely reflects the between month increase in evaporation, as well as potentially greater seawater intrusion or reduced freshwater dilution. This variation highlights the dynamic nature of marsh ecosystems and the significant role that tidal and seasonal processes play in shaping the physicochemical conditions present within tidal marshes, including spatial patterns in porewater salinity. The lack of significant differences in porewater salinity between upper and lower S. alterniflora zones, particularly at site B, suggests that the tidal influence at site B may have been less frequent, likely due to the proximity to the forest edge, leading to less frequent inundation of these areas. This could explain the smaller changes in salinity levels, especially in comparison to site A. We observed that plant height tended to be lower at porewater salinity levels above 18 psu, while salinity variations below this threshold were associated with relatively consistent plant height (Fig. 3 c). This pattern indicates a potential tolerance limit for salinity, beyond which plant growth was negatively impacted. However, it is important to note that porewater concentrations are the cumulative result of local consumption, production, and transport processes throughout plant development (Krask et al., 2022 ). Additionally, the availability of nutrients, particularly nitrogen in the form of ammonium (NH 4 ), has been shown to significantly influence plant growth in southeastern US salt marshes (Hopkinson & Schubauer, 1984 ; Mendelssohn & Morris, 2002 ). The more frequent tidal flooding near the creek bank leads to regular flushing of the porewater, resulting in more oxidized soil conditions (Krask et al., 2022 ). This environment facilitates the uptake of available nutrients by plants, potentially leading to taller plants in these areas. Given these complexities, inferring the specific physiological mechanisms involved in how plants respond to salt stress is challenging. While salinity is a critical factor, the interplay of nutrient dynamics, soil conditions, and hydrological processes plays a significant role in plant growth and adaptation to environmental stressors and is an important consideration when strategizing species management in S. alterniflora habitat (Chambers et al., 1998 ). Our findings were consistent with previous studies, which showed that tall-form S. alterniflora dominated near creek banks, while short-form S. alterniflora was more prevalent upslope towards the forest edge (Mendelssohn, 1979 ; Craft et al., 1991 ; Koretsky et al., 2008 ; Negrin et al., 2011 ). The decrease in panicle numbers in upper S. alterniflora zones in both sites, although only significant for site B, may be attributed to the fact that the plots in Site B were closer to the forest edge and may have greater exposure to freshwater discharge, which introduced a greater salinity gradient or more frequent exposure to freshwater sheet flow from the adjacent upland area. Similar to plant height, we found that higher salinity levels were associated with shorter panicle length when the salinity exceeded 18 psu, while panicle length remained relatively consistent by salinity changes below this threshold. The observed changes in plant height, panicle number, and panicle length with increasing salinity indicated that these plants may have specific salinity tolerance thresholds. Beyond these thresholds, plant growth and reproductive features were negatively impacted. The variations in these phenotypic traits in response to salinity stress suggest that plants have developed adaptive strategies to cope with high salinity. These likely involved physiological adaptations such as altering water uptake mechanisms, ion regulation, and osmotic balance to maintain growth and reproduction under saline conditions. The relationship between panicle number and length to porewater salinity was particularly indicative of how salinity stress relates to plant reproductive strategies. Fewer and shorter values for these traits under high-salinity conditions could signify a trade-off where plants allocated more resources toward survival rather than reproduction. These patterns reflected the ecological dynamics of marsh ecosystems, where salinity is a key environmental factor influencing plant community structure and function (Pennings & Bertness, 2001 ). Changes in plant growth and reproductive traits relative to salinity could have cascading effects on ecosystems because of the importance of the structured habitat provided by the stems of marsh vegetation (Lewis & Eby, 2002 ; Lefcheck et al., 2019 ). Future studies should consider plant density across the elevation gradients and zones to consider potential trade-offs exemplified by the self-thinning law in S. alterniflora (Liu & Pennings, 2019 ). Our investigation revealed consistent C:N ratio across the elevation and salinity gradients (Fig. 6 ), a slight decrease in C:N across in site B and no significant differences in foliar carbon and nitrogen concentrations between the lower and upper marsh for either site (Fig. 7 ). Although elevated salinity can alter nitrogen assimilation (Bradley & Morris, 1992 ), the absence of detectable shifts suggests one or more buffering mechanisms: (1) microbial and sediment processes that stabilize plant-available N across zones; (2) co-limitation by other nutrients (e.g., P or micronutrients) constraining N assimilation independently of salinity; and (3) hydrologic decoupling whereby surface salinity poorly indexes root-zone exposure. To evaluate these mechanisms, we recommend: (1) repeated porewater measurements of electrical conductivity (EC) together with dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) across tidal/rainfall cycles; (2) pairing foliar C:N with N:P to analyze nutrient limitation and N sources; and (3) mixed-effects modeling with site/zone as random effects, reporting effect sizes with 95% CIs and an a priori power analysis to state minimum detectable differences. Our study highlights the complex interactions between salinity and elevation in shaping growth and reproductive traits of the dominant plant within salt marshes along much of the Atlantic coast of the U.S., S. alterniflora . The observed variations in plant height, panicle number, and in response to salinity underscore the significance of understanding how these traits are influenced by changing environmental conditions. The adaptive strategies plants employ, including alterations in nutrient uptake and osmotic regulation, are crucial for their survival and reproduction in saltmarsh ecosystems. Given the increasing challenges posed by sea-level rise, as well as shifting storm patterns and associated precipitation, it is essential to further investigate these trait variations and the mechanisms that drive their expression across sites. This knowledge will enhance our understanding of plant adaptability and resilience and inform the management and conservation of coastal ecosystems, where plant community structure and function are tightly linked to environmental stressors. Declarations Ethics approval and consent to participate: No permissions for plant collections were required. Consent for publication: Not applicable. Funding: This work was partially funded by Clemson University Faculty SUCCEEDS program and Charles Carter Newman Endowment funds, Clemson University, Clemson, SC. Funding for RPD was provided by the United States NOAA Office for Coastal Management via the annual operating award to the North Inlet-Winyah Bay NERR (NA21NOS420039). Authors' contributions: LRO, QS and RK conceptualized the study and methods and planned the execution of data collection. LRO, JAR and RPD conducted the field data collection. LRO and QS synthesized, quality controlled and analysed the data and wrote the results and discussion. All authors contributed to the final writing of the manuscript and approved its final stage. Acknowledgements The authors would like to thank Shelby Rowland for her contributions to field work and data collection, as well as the NI-WB NERR staff for construction and maintenance of marsh boardwalk infrastructure. This work was partially funded by Clemson University Faculty SUCCEEDS program and Charles Carter Newman Endowment funds, Clemson University, Clemson, SC. Funding for RPD was provided by the United States NOAA Office for Coastal Management via the annual operating award to the North Inlet-Winyah Bay NERR (NA21NOS420039). Availability of data and material: The datasets during and/or analysed during the current study available from the corresponding author on reasonable request. 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Tidal wetland stability in the face of human impacts and sea-level rise. Nature , 504(7478), 53–60. https://doi.org/10.1038/nature12856 Koretsky, C. M., Haveman, M., Cuellar, A., Beuving, L., Shattuck, T., & Wagner, M. (2008). Influence of Spartina and Juncus on Saltmarsh Sediments. I. Pore Water Geochemistry. Chemical Geology , 255(1), 87–99. https://doi.org/10.1016/j.chemgeo.2008.06.013 Krask, J. L., Buck, T. L., Dunn, R. P., & Smith, E. M. (2022). Increasing tidal inundation corresponds to rising porewater nutrient concentrations in a southeastern U.S. salt marsh. PLOS ONE , 17(11), e0278215. https://doi.org/10.1371/journal.pone.0278215 Lefcheck, J. S., Hughes, B. B., Johnson, A. J., Pfirrmann, B. W., Rasher, D. B., Smyth, A. R., Williams, B. L., Beck, M. W., & Orth, R. J. (2019). Are coastal habitats important nurseries? A meta-analysis. Conservation Letters , 12(4), e12645. https://doi.org/10.1111/conl.12645 Lewis, D. B., & Eby, L. A. (2002). Spatially heterogeneous refugia and predation risk in intertidal salt marshes. Oikos , 96(1), 119–129. https://doi.org/10.1034/j.1600-0706.2002.960113.x Lin, L., Liu, W., Zhang, M., Lin, X., Zhang Y., & Tian, Y. (2019). Different Height Forms of Spartina alterniflora Might Select Their Own Rhizospheric Bacterial Communities in Southern Coast of China. Microbial Ecology 77, 124–135. https://doi.org/10.1007/s00248-018-1208-y Liu, W., & Pennings, S.C. (2019). Self-thinning and size-dependent flowering of the grass Spartina alterniflora across space and time. Functional Ecology , 33(10), 1830-1841. https://doi.org/10.1111/1365-2435.13384 Mann, H. B., & Whitney, D. R. (1947). On a Test of Whether One of Two Random Variables is Stochastically Larger than the Other. The Annals of Mathematical Statistics , 18(1), 50–60. http://www.jstor.org/stable/2236101 Mendelssohn, I. A. (1979). Nitrogen Metabolism in the Height Forms of Spartina alterniflora in North Carolina. Ecology 60(3), 574–584. https://doi.org/10.2307/1936078 Mendelssohn, I. A., & Morris, J. T. (2002). Eco-Physiological Controls on the Productivity of Spartina alterniflora Loisel. In Concepts and Controversies in Tidal Marsh Ecology , ed. M. P. Weinstein and D. A. Kreeger, 59–80. Springer, Dordrecht. https://doi.org/10.1007/0-306-47534-0_5 Minello, T. J., Rozas, L. P., & Baker, R. (2012). Geographic Variability in Salt Marsh Flooding Patterns may Affect Nursery Value for Fishery Species. Estuaries and Coasts , 35, 501–514. https://doi.org/10.1007/s12237-011-9463-x Minello, T. J., & Webb, J. W. (1997). Use of natural and created Spartina alterniflora salt marshes by fishery species and other aquatic fauna in Galveston Bay, Texas, USA. Marine Ecology Progress Series , 151, 165–179. https://doi.org/10.3354/meps151165 Morris, J., Sundareshwar, P., Nietch, C., Kjerfve, B., & Cahoon, D. (2002). Responses of Coastal Wetlands to Rising Sea Level. Ecology , 83(10), 2869–2877. https://doi.org/10.2307/3072022 Mounger, J. M., van Riemsdijk, I., Boquete, M. T., Wagemaker, C. A. M., Fatma, S., Robertson, M. H., Voors, S. A., Oberstaller, J., Gawehns, F., Hanley, T. C., Grosse, I., Verhoeven, K. J. F., Sotka, E. E., Gehring, C. A., Hughes, A. R., Lewis, D. B., Schmid, W., & Richards, C. L. (2022). Genetic and Epigenetic Differentiation Across Intertidal Gradients in the Foundation Plant Spartina alterniflora . Frontiers in Ecology and Evolution , 10. https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2022.868826 Negrin, V. L., Spetter, C. V., Asteasuain, R. O., Perillo, G. M. E., & Marcovecchio, J. E. (2011). Influence of flooding and vegetation on carbon, nitrogen, and phosphorus dynamics in the pore water of a Spartina alterniflora salt marsh. Journal of Environmental Sciences , 23(2), 212–221. https://doi.org/10.1016/S1001-0742(10)60395-6 Normile, D. (2004). Expanding Trade With China Creates Ecological Backlash. Science , 306(5698), 968–969. https://doi.org/10.1126/science.306.5698.968 O’Connell, J. L., Alber, M., & Pennings, S. C. (2020). Microspatial Differences in Soil Temperature Cause Phenology Change on Par with Long-Term Climate Warming in Salt Marshes. Ecosystems , 23(3), 498–510. https://doi.org/10.1007/s10021-019-00418-1 Ornes, W., & Kaplan, D. (1989). Macronutrient status of tall and short forms of Spartina alterniflora in a South Carolina salt marsh. Marine Ecology Progress Series , 55, 63–72. https://doi.org/10.3354/meps055063 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 03 Apr, 2026 Reviewers invited by journal 03 Apr, 2026 Editor invited by journal 27 Mar, 2026 Editor assigned by journal 25 Mar, 2026 First submitted to journal 24 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9214713","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":617245806,"identity":"1810114e-0878-4d42-9952-f6b70a49081f","order_by":0,"name":"Lydia O'Halloran","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA00lEQVRIiWNgGAWjYBACPgYeBoYHBQxyDOxwsQT8WthAWhIMGIwZmEnVkthAvBb23oMfEgxs0vubmY9u/FFxh4GfPccAvxaec8kSCQZpuTMOs6Xd5jnzjEGy5w0BLRI5BkAth3M3MPOY3WZsO8xgcIOQLRI5xj+AWtINmPm/3fwJ1GJPhBYzkC0JBsw8bDd4QbZIEPTLGTMLoF8MgX4xA/rlMI/EmWcFeLXws/cY3/hQYSPP39787OaPisNy/O3JG/BqwQA8pCkfBaNgFIyCUYAVAADUjUCv1S/Q8wAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-3634-9696","institution":"Clemson University College of Agriculture Forestry and Life Sciences","correspondingAuthor":true,"prefix":"","firstName":"Lydia","middleName":"","lastName":"O'Halloran","suffix":""},{"id":617245807,"identity":"22068e06-f98a-46f0-ad5e-11740e0fc0b7","order_by":1,"name":"Qiong Su","email":"","orcid":"","institution":"Clemson University College of Agriculture Forestry and Life Sciences","correspondingAuthor":false,"prefix":"","firstName":"Qiong","middleName":"","lastName":"Su","suffix":""},{"id":617245808,"identity":"ac18c3a2-24e2-44f8-ab99-0e8f97ebe382","order_by":2,"name":"Robert Dunn","email":"","orcid":"","institution":"North Inlet-Winyah Bay NEER","correspondingAuthor":false,"prefix":"","firstName":"Robert","middleName":"","lastName":"Dunn","suffix":""},{"id":617245809,"identity":"4684c019-6602-47b5-9c90-15a8a29570d8","order_by":3,"name":"Justin Robbins","email":"","orcid":"","institution":"Clemson University College of Agriculture Forestry and Life Sciences","correspondingAuthor":false,"prefix":"","firstName":"Justin","middleName":"","lastName":"Robbins","suffix":""},{"id":617245810,"identity":"b251e6d3-fe17-45b8-9088-9aa20030b37f","order_by":4,"name":"Raghupathy Karthikeyan","email":"","orcid":"","institution":"Clemson University College of Agriculture Forestry and Life Sciences","correspondingAuthor":false,"prefix":"","firstName":"Raghupathy","middleName":"","lastName":"Karthikeyan","suffix":""}],"badges":[],"createdAt":"2026-03-24 17:05:50","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9214713/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9214713/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106515354,"identity":"d0b99e3e-d385-4de9-ba0d-cdb8ee7715e9","added_by":"auto","created_at":"2026-04-09 11:43:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":615115,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Location of the two sites (A and B) at the North Inlet-Winyah Bay National Estuarine Research Reserve research site in Georgetown, SC and example sampling point. (b) Elevation profiles of the 3 transects across sites A (blue) and B (red). Note: The North American Vertical Datum of 1998 (NAVD 88) was used as the reference level. Each site contained 3 transects (Site A: A1, A2, A3; Site B: B1, B2, B3). Permanent plots were grouped into upper-elevation and lower-elevation marsh zones based on elevation and distance from the forest edge using k-means clustering.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/862b508e791114a20102b7de.png"},{"id":106515355,"identity":"49564553-e589-459c-888a-f2ee43987fe1","added_by":"auto","created_at":"2026-04-09 11:43:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1364982,"visible":true,"origin":"","legend":"\u003cp\u003ePorewater salinity variations with elevation. (a, b) Changes in elevation and salinity in (c, d) May and (e, f) June in upper-elevation and lower-elevation marsh zones, and porewater salinity variations in (g-j) for May and June in Sites A and B. The black dots in the boxes are the means, and boxplots show the 25th, 50th, 75th percentiles and extremes. \"ns\" represents a nonsignificant difference at the 0.05 level, and the \u003cem\u003ep value\u003c/em\u003e is shown in parentheses. \"*, **, ***, and ****\" represent significance at the 0.05, 0.01, 0.001, and 0.0001 probability levels, respectively, according to the Wilcoxon rank-sum (Mann–Whitney) test. The shaded areas in (g-j) indicate the 95% confidence intervals (CIs) for the dose-response curves. Trends (slopes) were calculated at the \u003cem\u003ep\u003c/em\u003e\u0026lt; 0.05 probability level using Student’s\u003cem\u003e t\u003c/em\u003e test. (Each point was averaged based on 4 replicate measurements.)\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/da572a08dd4187241c9e1b4f.png"},{"id":106724995,"identity":"a875c1de-daf1-431c-8bb3-ae5c34a141ad","added_by":"auto","created_at":"2026-04-12 18:30:56","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1297601,"visible":true,"origin":"","legend":"\u003cp\u003ePlant height variations with elevation and porewater salinity. (a, b) Plant height changes by marsh zone and plant height variations withelevation (c, d) and porewater salinity (e, f) for sites A and B. The black dots in the boxes are the means, and the boxplots show the 25th, 50th, 75th percentiles and extremes. \"ns\" represents a nonsignificant difference at the 0.05 level, and the \u003cem\u003ep value\u003c/em\u003e is shown in parentheses. \"*, **, ***, and ****\" represent significance at the 0.05, 0.01, 0.001, and 0.0001 probability levels, respectively, according to the Wilcoxon rank-sum (Mann–Whitney) test. The shaded areas in (c-f) indicate the 95% confidence intervals (CIs) for the dose-response curves.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/e9de41221ec2710bc494b1d6.png"},{"id":106515359,"identity":"4893519e-524e-4041-86b8-9fd1de2a1191","added_by":"auto","created_at":"2026-04-09 11:43:26","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1184281,"visible":true,"origin":"","legend":"\u003cp\u003ePanicle number variations with elevation and porewater salinity. (a, b) Panicle number changes in upper-elevation and lower-elevation marsh zones and panicle number variations withelevation (c, d) and porewater salinity (e, f) for Sites A and B. The black dots in the boxes are the means, and the boxplots show the 25th, 50th, 75th percentiles and extremes. \"ns\" represents a nonsignificant difference at the 0.05 level, and the \u003cem\u003ep value\u003c/em\u003e is shown in parentheses. \"*, **, ***, and ****\" represent significance at the 0.05, 0.01, 0.001, and 0.0001 probability levels, respectively, according to the Wilcoxon rank-sum (Mann–Whitney) test. The shaded areas in (c-f) indicate the 95% confidence intervals (CIs) for the dose-response curves.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/d378048ab93ce97b11596775.png"},{"id":106515360,"identity":"f5f7cde4-b7ae-449b-a8f0-0a09c52cc605","added_by":"auto","created_at":"2026-04-09 11:43:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1187962,"visible":true,"origin":"","legend":"\u003cp\u003ePanicle length variations with elevation and porewater salinity. (a, b) Panicle length changes in upper-elevation and lower-elevation marsh zones and panicle length variations withelevation (c, d) and porewater salinity (e, f) for Sites A and B. The black dots in the boxes are the means, and the boxplots show the 25th, 50th, 75th percentiles and extremes. \"ns\" represents a nonsignificant difference at the 0.05 level, and the \u003cem\u003ep value\u003c/em\u003e is shown in parentheses. \"*, **, ***, and ****\" represent significance at the 0.05, 0.01, 0.001, and 0.0001 probability levels, respectively, according to the Wilcoxon rank-sum (Mann–Whitney) test. The shaded areas in (c-f) indicate the 95% confidence intervals (CIs) for the dose-response curves.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/77f3f34e665344d345c80c89.png"},{"id":106724877,"identity":"2bc0c8a2-6263-4179-9f5c-6391f97e02c7","added_by":"auto","created_at":"2026-04-12 18:30:14","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1112309,"visible":true,"origin":"","legend":"\u003cp\u003eC:N ratio variations with elevation and porewater salinity. (a, b) C:N ratio changes in upper-elevation and lower-elevation marsh zones, and C:N ratio variations with elevation (c, d) and porewater salinity (e, f) for sites A and B. The black dots in the boxes are the means, and the boxplots show the 25th, 50th, 75th percentiles and extremes. \"ns\" represents a nonsignificant difference at the 0.05 level, and the \u003cem\u003ep value\u003c/em\u003eis shown in parentheses. \"*, **, ***, and ****\" represent significance at the 0.05, 0.01, 0.001, and 0.0001 probability levels, respectively, according to the Wilcoxon rank-sum (Mann–Whitney) test. The shaded areas in (c-f) indicate the 95% confidence intervals (CIs) for the dose-response curves.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/ff2cb3e7102dc33006624b6a.png"},{"id":106515357,"identity":"43ad32b2-93e2-43c7-a427-40ccbc33fad9","added_by":"auto","created_at":"2026-04-09 11:43:26","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":756823,"visible":true,"origin":"","legend":"\u003cp\u003e(a, b) Carbon content, and (c,d) nitrogen content in upper-elevation and lower-elevationmarsh zones. The black dots in the boxes are the means, and the boxplots show the 25th, 50th, 75th percentiles and extremes. \"ns\" represents a nonsignificant difference at the 0.05 level, and the \u003cem\u003ep value\u003c/em\u003e is shown in parentheses.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/92a91442b289ec7180dec0e8.png"},{"id":106959407,"identity":"0478a8ca-dba9-411a-8573-be630dbd38db","added_by":"auto","created_at":"2026-04-15 09:08:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8146292,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9214713/v1/dc8201dd-c2a0-4d80-8f29-b11fe2d0db66.pdf"}],"financialInterests":"","formattedTitle":"Trait variability in a widespread and dominant salt marsh grass in a South Carolina estuary","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSalt marshes are highly productive coastal ecosystems that provide essential ecological functions such as carbon sequestration, shoreline stabilization, and habitat provisioning, and support valuable services including tourism and commercial fisheries (Barbier et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Purcell et al., \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Salt marsh plant communities experience a range of environmental conditions and disturbances due to tidal flooding, salt deposition, upland runoff and storms. The plant communities in these environments are adapted to growing in these harsh conditions as reflected in morphological differences along environmental gradients found in salt marshes (Pennings \u0026amp; Bertness, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2001\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOne of the defining features of coastal salt marsh ecosystems is the elevation gradient, which has been well-documented in terms of its effects on inundation, salinity, and plant zonation (Pennings \u0026amp; Bertness, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Across this gradient, plant productivity has been shown to increase from low to high elevations (Morris et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) while plant species distribution can be limited by both salinity and interspecific competition across the gradient (Pennings et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Along the Atlantic and Gulf coasts in the southeastern United States, \u003cem\u003eSpartina alterniflora\u003c/em\u003e is a dominant C4 grass species adapted to saline and anoxic conditions across the salt marsh elevation gradient. \u003cem\u003eS. alterniflora\u003c/em\u003e is native to the U.S. Atlantic coast but considered invasive in salt marshes in other regions (Ayres et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; Normile, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). The root and rhizome structures of \u003cem\u003eS. alterniflora\u003c/em\u003e help stabilize soils during storm and high tide events (Cahoon et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and, as such, are an integral part of coastal ecosystems that provides habitat for a diverse and productive community of salt marsh-affiliated species (Minello \u0026amp; Webb, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Minello et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2012\u003c/span\u003e), which can also vary across the marsh platform elevation gradient (Dunn et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSoutheastern coastal ecosystems are experiencing stressors from press and pulse disturbances (IPCC, 2023; Harris et al., 2018) which can impact salt marsh vegetation in multiple ways. In the case of \u003cem\u003eS. alterniflora\u003c/em\u003e marshes, increased inundation time from sea level rise over a 10-year period resulted in a 0.94% reduction of belowground biomass (Runion et al., \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Warming winter soils are a main driver for earlier \u003cem\u003eS. alterniflora\u003c/em\u003e green-up times (O\u0026rsquo;Connell et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) and warming air temperatures can shift plants towards more clonal reproduction and less sexual reproduction (Jiang et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Extreme hurricane-related pulse events resulted in mass \u003cem\u003eS. alterniflora\u003c/em\u003e dieback due to flooding and extreme precipitation (Stagg et al., \u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Salt marsh vegetation can help mitigate erosional losses from sea level rise and more frequent storm events through soil accretion by adding organic matter and helping retain mineral soil (Morris et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Cahoon et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Nevertheless, their functional role in the ecosystem assumes their own ability to persist through changing conditions. Marsh vegetation productivity may increase with rising mean annual temperatures, potentially offsetting erosional losses (and associated vegetation) from sea-level rise in some locations (Kirwan et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). However, marshes' elevation gains through soil accretion are predicted to lag behind the pace of sea-level rise (Crosby et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), a trend that could be exacerbated or ameliorated by further human impacts (Kirwan \u0026amp; Megonigal, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The fate of these marshes will partially depend upon the resiliency and adaptability of the plant species that live there, particularly dominant species such as \u003cem\u003eS. alterniflora\u003c/em\u003e.\u003c/p\u003e \u003cp\u003ePlant trait variation is an important quality that reflects adaptation and potential resilience to abiotic drivers. For example, \u003cem\u003eS. alterniflora\u003c/em\u003e grows in short form and tall form, differing in plant height along the marsh platform. Tall form plants grow near creek edges where elevation is lower and inundation by the tide is more frequent. Short form plants grow at higher elevations but also occur in heterogeneous patches across the salt marsh platform. \u003cem\u003eS. alterniflora\u003c/em\u003e exhibits these different growth forms based on marsh location (intertidal zone vs. panne; Shea et al., \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e1975\u003c/span\u003e) and nutrient supply (Valiela et al., \u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e1978\u003c/span\u003e), with both factors potentially influencing growth form simultaneously. Further evidence attributes the distribution of different growth forms to plant macronutrient concentrations (Ornes \u0026amp; Kaplan, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e1989\u003c/span\u003e) and salinity (Pennings \u0026amp; Bertness, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Lin et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) examined rhizosphere bacterial community composition in the field and in a common garden, supporting studies like Valiela et al. (\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e2023\u003c/span\u003e), which show that nitrogen abundance promotes the tall form. Although abiotic factors are correlated with \u003cem\u003eS. alterniflora\u003c/em\u003e height, studies like Gallagher et al. (\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1988\u003c/span\u003e), Seliskar et al. (\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e2002\u003c/span\u003e), and Zerebecki et al. (2021) show persistent trait expression amid transplantation, confirming that height is a result of both environmental and genetic factors (Anderson \u0026amp; Treshow, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1980\u003c/span\u003e), as well as epigenetic factors (Mounger et al., 2022).\u003c/p\u003e \u003cp\u003eMany studies of \u003cem\u003eS. alterniflora\u003c/em\u003e have focused on variation in plant height across the marsh platform, but other morphological and fitness-related traits may also be important for understanding how this species may respond to current and predicted environmental changes (IPCC, 2023). In particular, the relationship between growth form (tall vs. short) and reproductive traits, such as panicle length and number, remains unclear. For example, inflorescence length, which is correlated with flowering stem height (Crosby et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), may differ between growth forms and across the marsh platform. However, environmental stressors such as salinity and flooding, more intense at lower elevations near creek edges, may suppress reproductive output, potentially obscuring trait relationships. For example, panicle number, an indicator of plant health in other \u003cem\u003ePoaceae\u003c/em\u003e species, decreases under salt stress (Razzaq et al., 2020). If this holds for \u003cem\u003eS. alterniflora\u003c/em\u003e, we expect panicle number to be lower under salinity stress, such as at creek edges, even though larger plant size in these areas might otherwise suggest greater reproductive output. In addition to reproductive traits, physiological indicators of stress, such as foliar C:N, which may reflect reduced nitrogen uptake under salinity stress (Bradley \u0026amp; Morris, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e1991\u003c/span\u003e), could also decrease across the marsh platform and provide further insight into how \u003cem\u003eS. alterniflora\u003c/em\u003e responds to environmental gradients.\u003c/p\u003e \u003cp\u003eThis study investigates how panicle number, panicle length, plant height and foliar nutrient concentrations vary along salt marsh platforms in local \u003cem\u003eS. alterniflora\u003c/em\u003e populations. This study tested the hypothesis that elevation and salinity gradients across the marsh platform drive corresponding variations in \u003cem\u003eS. alterniflora\u003c/em\u003e phenotypic traits, with plants at the lower elevation (higher salinity) exhibiting lower reproductive output including shorter height, shorter and fewer panicles, and higher C:N relative to those in higher elevations (lower salinity). To test this hypothesis, plant height, panicle length and number, and foliar nutrient concentrations were measured across the marsh platform at two salt marsh sites in coastal South Carolina.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003eSite description, elevation and porewater salinity\u003c/p\u003e \u003cp\u003eThis study examined variation in \u003cem\u003eS. alterniflora\u003c/em\u003e traits within a representative back-barrier salt marsh in the North Inlet-Winyah Bay National Estuarine Research Reserve in Georgetown, SC, USA (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The North Inlet estuary is an ocean-dominated system with long-term mean salinities in tidal creeks\u0026thinsp;\u0026gt;\u0026thinsp;30 psu. Freshwater input into this estuary is via shallow groundwater and surface flows from the surrounding watershed during precipitation events. We collected data from 2 distinct sites within a contiguous salt marsh along Crabhaul Creek, an intertidal creek on the western edge of the North Inlet estuary. Our study sites are approximately 2 km apart; each site includes 3 replicate transects (~\u0026thinsp;210 m long at Site A, ~\u0026thinsp;75 m long Site B) running from the creek bank to the upland forest edge. Within each of these 6 transects, data on plant traits and marsh biogeochemical conditions were collected from permanently established plots where \u003cem\u003eS. alterniflora\u003c/em\u003e was present along the elevation gradient. The number of permanent plots containing \u003cem\u003eS. alterniflora\u003c/em\u003e was 4 for Site A and 6 for Site B. Permanent plots were grouped into upper-elevation and lower-elevation marsh zones using a k-means clustering (k\u0026thinsp;=\u0026thinsp;2) on elevation (m; NAVD88) and distance to the forest edge (m). Clustering was run separately for each site. Prior to clustering, both variables were z-standardized to equalize scale. While these two sites are both \u003cem\u003eS. alterniflora\u003c/em\u003e-dominated salt marshes with similar tidal inundation frequencies (low marsh plots inundated\u0026thinsp;\u0026gt;\u0026thinsp;40% of the time across both sites; Krask et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), they differ in ways that could play a role in plant phenotypic expression. Namely, Site B has a steeper slope due to the narrower marsh platform; Site B is also exhibiting a more uniform reduction in porewater salinity through time while salinity changes are patchier at Site A (Krask et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Both sites are experiencing long-term increases in inundation, with plots adjacent to the creekbank showing the highest rates of change in inundation time (Krask et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOrthometric height (elevation, in m) of each plot was measured in 2021 with a Trimble R8s real-time kinematic global positioning system (RTK-GPS) and referenced to the North American Vertical Datum of 1988 (NAVD 88). Plot-level elevation values used here are calculated from triplicate measurements made in opposite corners and within the center of each plot in the field.\u003c/p\u003e \u003cp\u003eSediment porewater salinity at each plot was measured in May and June 2023. Specifically, porewater samples were collected in triplicate from each plot during each month at a sampling depth of 25 cm. Porewater was collected using modified diffusion equilibrators, which were 20mL glass scintillation vials filled with deionized water and covered with nitex mesh (20 \u0026micro;m) membranes secured with an open-topped screw cap. Vials were housed inside porous PVC pipes embedded into the marsh sediment, and vials were left to equilibrate for approximately one month. Upon retrieval, vials were capped and returned to the lab on ice and processed immediately. Salinity was measured with a handheld Mettler-Toledo Seven2Go pro conductivity/salinity probe, and replicate samples were averaged to generate plot-level mean values.\u003c/p\u003e \u003cp\u003ePhenotypic traits\u003c/p\u003e \u003cp\u003eAlong each of the six transects, vegetation measurements were repeated within each 1-m\u003csup\u003e2\u003c/sup\u003e permanent plot in the first week of September 2023. Plant height was identified as non-destructive measurements of the season\u0026rsquo;s growth success. Plant height was measured for four randomly selected flowering plants within each permanent plot. The total number of \u003cem\u003eS. alterniflora\u003c/em\u003e panicles were counted within each permanent plot where \u003cem\u003eS. alterniflora\u003c/em\u003e was present (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). Panicle length was determined as the mean of four randomly selected panicles measured within each permanent plot. Leaf nutrient concentration was measured from leaves collected during the same period. Five randomly selected leaf samples were collected from individual plants in each permanent plot. Leaves were dried at 60 \u0026ordm;C for 48 hours, ground with a Wiley mill and analyzed for carbon and nitrogen content using a LECO elemental analysis instrument (LECO Corporation, USA).\u003c/p\u003e \u003cp\u003eStatistical analyses\u003c/p\u003e \u003cp\u003eWithin each site, upper- and lower-zone observations were compared using the Wilcoxon rank-sum (Mann\u0026ndash;Whitney) test (two-sided) (Mann \u0026amp; Whitney, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1947\u003c/span\u003e). Dose‒response curves (Poorter et al., \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Poorter et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) were constructed to analyze the salinity variations with elevation at each site and the responses of plant height, panicle number, panicle length, and foliar nutrients (CN ratio, carbon content, and nitrogen content) to elevation and salinity changes. Here, local regression (loess), a nonparametric method, was employed to fit the dose‒response curve. Linear regressions were used to assess the trends of these parameters in response to elevation and salinity. Statistical significance of the trends (regression slopes) was evaluated at the α\u0026thinsp;\u003cem\u003e=\u003c/em\u003e\u0026thinsp;0.05 probability level using Student\u0026rsquo;s \u003cem\u003et\u003c/em\u003e test. All the analyses were performed using Python 3.11.6 (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://docs.python.org/release/3.11.6/\u003c/span\u003e\u003cspan address=\"https://docs.python.org/release/3.11.6/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eElevation and porewater salinity\u003c/p\u003e \u003cp\u003eThe transects at sites A and B exhibited similar elevation ranges despite their varying distances from the forest edge to the creek bank (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). Specifically, plots with \u003cem\u003eS. alterniflora\u003c/em\u003e at site A spanned 126 to 267 m from the forest edge, covering elevations from \u0026minus;\u0026thinsp;0.140 to 0.514 m. In contrast, plots with \u003cem\u003eS. alterniflora\u003c/em\u003e in site B were closer to the forest edge, ranging from 10 to 78 m away, and covered elevations between 0.028 and 0.524 m. The upper-elevation \u003cem\u003eS. alterniflora\u003c/em\u003e zones identified by k-means clustering within sites A (0.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12 m) and B (0.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 m) had similar mean elevations, but the lower-elevation zone in site A (0.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 m) was significantly lower than that in site B (0.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 m; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, b).\u003c/p\u003e \u003cp\u003eSediment porewater salinity did not significantly differ between the upper and lower \u003cem\u003eS. alterniflora\u003c/em\u003e zones across the two sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec-f). In the low-elevation plots closest to the creek bank, the mean porewater salinities were slightly greater (by 0.2\u0026ndash;0.6 psu) than those in the upper-elevation plots, except for site A in June. Furthermore, no significant trends in porewater salinity correlated with increasing elevation except for site A in June (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). Notably, a linear increase in porewater salinity with elevation was observed for site A in June, at a rate of 5.7 psu per meter (p\u0026thinsp;=\u0026thinsp;0.007, n\u0026thinsp;=\u0026thinsp;11) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). The porewater salinities in both sites were greater in June than in May (p\u0026thinsp;=\u0026thinsp;0.006), with increases of 2.7 psu in Site A and 1.3 psu in Site B mean salinity values.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePhenotypic traits\u003c/p\u003e \u003cp\u003eWe observed a marked difference in plant height across the different marsh zones. Specifically, there was a 44% reduction in plant height transitioning from the lower- to upper-elevation \u003cem\u003eS. alterniflora\u003c/em\u003e zone in Site A (p\u0026thinsp;\u003cem\u003e=\u0026thinsp;0.06\u003c/em\u003e) and a 37% reduction in Site B (p\u0026thinsp;=\u0026thinsp;0.0002) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, b). Additionally, we found significant linear decreases in plant height with increasing elevation in both sites, with values of \u0026minus;\u0026thinsp;195 cm per meter of elevation gain in Site A and \u0026minus;\u0026thinsp;180 cm per meter in Site B (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, d). The decreasing trends suggested a strong correlation between elevation and plant height, particularly at relatively lower elevations (i.e., \u0026lt;\u0026thinsp;0.35 m; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). We also found that when the salinity exceeded 18 psu plant height was lower as seen in site A (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTotal panicle numbers did not differ between marsh zones in either site (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, b). The fluctuations in panicle numbers in Site B appeared more acutely responsive to variations in salinity than did those in Site A (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee, f), with a significant reduction of 1.1 panicles per unit increase in salinity (p\u0026thinsp;=\u0026thinsp;0.043, n\u0026thinsp;=\u0026thinsp;18).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePanicle length exhibited patterns similar to those of plant height in response to variations in elevation and porewater salinity. Panicle length did not vary between lower and upper \u003cem\u003eS. alterniflora\u003c/em\u003e zones at site A (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) but there was a significant decrease of nearly 25% in site B (p\u0026thinsp;=\u0026thinsp;0.002) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). We also found linear decreases in panicle length with increasing elevation for both sites, with decreasing values of \u0026minus;\u0026thinsp;19.8 cm per meter (p\u0026thinsp;=\u0026thinsp;0.020, n\u0026thinsp;=\u0026thinsp;11) (site A; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec) and \u0026minus;\u0026thinsp;16.0 cm per meter (p\u0026thinsp;=\u0026thinsp;0.001, n\u0026thinsp;=\u0026thinsp;18) (site B; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). Panicle length also decreased across the salinity gradient at site A (p\u0026thinsp;=\u0026thinsp;0.002, n\u0026thinsp;=\u0026thinsp;11) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFoliar nutrients\u003c/p\u003e \u003cp\u003eOur investigation revealed no relationship between foliar carbon-to-nitrogen (C:N) ratios with elevation (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Site B exhibited a negative relationship between C:N and salinity (p\u0026thinsp;=\u0026thinsp;0.027, n\u0026thinsp;=\u0026thinsp;18) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef). There were no differences between foliar carbon, or nitrogen concentrations between the lower and upper zones (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eBased on replicated sampling during the growing season, we find that \u003cem\u003eS. alterniflora\u003c/em\u003e exhibits distinct variation in some demographic traits across both elevation and porewater salinity gradients within a representative salt marsh in the southeast United States. Importantly, other traits did not respond to changes in elevation or porewater salinity. Salt marsh sites A and B within the North Inlet-Winyah Bay NERR showed similarities in elevation ranges despite differences in their distances from the forest edge to the creek bank, demonstrating that local topography likely plays a significant role in shaping the elevation profiles of these sites. The transect along Site A was longer but with a similar elevation gain to site B. The significant difference in lower-elevation zones between site A and site B may indicate variations in tidal influence, which is further supported by the trend observed at site A, where higher elevations were associated with increased porewater salinity in June. The increase in porewater salinity observed in June compared to May across both sites likely reflects the between month increase in evaporation, as well as potentially greater seawater intrusion or reduced freshwater dilution. This variation highlights the dynamic nature of marsh ecosystems and the significant role that tidal and seasonal processes play in shaping the physicochemical conditions present within tidal marshes, including spatial patterns in porewater salinity. The lack of significant differences in porewater salinity between upper and lower \u003cem\u003eS. alterniflora\u003c/em\u003e zones, particularly at site B, suggests that the tidal influence at site B may have been less frequent, likely due to the proximity to the forest edge, leading to less frequent inundation of these areas. This could explain the smaller changes in salinity levels, especially in comparison to site A.\u003c/p\u003e \u003cp\u003eWe observed that plant height tended to be lower at porewater salinity levels above 18 psu, while salinity variations below this threshold were associated with relatively consistent plant height (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). This pattern indicates a potential tolerance limit for salinity, beyond which plant growth was negatively impacted. However, it is important to note that porewater concentrations are the cumulative result of local consumption, production, and transport processes throughout plant development (Krask et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Additionally, the availability of nutrients, particularly nitrogen in the form of ammonium (NH\u003csub\u003e4\u003c/sub\u003e), has been shown to significantly influence plant growth in southeastern US salt marshes (Hopkinson \u0026amp; Schubauer, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1984\u003c/span\u003e; Mendelssohn \u0026amp; Morris, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). The more frequent tidal flooding near the creek bank leads to regular flushing of the porewater, resulting in more oxidized soil conditions (Krask et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This environment facilitates the uptake of available nutrients by plants, potentially leading to taller plants in these areas. Given these complexities, inferring the specific physiological mechanisms involved in how plants respond to salt stress is challenging. While salinity is a critical factor, the interplay of nutrient dynamics, soil conditions, and hydrological processes plays a significant role in plant growth and adaptation to environmental stressors and is an important consideration when strategizing species management in \u003cem\u003eS. alterniflora\u003c/em\u003e habitat (Chambers et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Our findings were consistent with previous studies, which showed that tall-form \u003cem\u003eS. alterniflora\u003c/em\u003e dominated near creek banks, while short-form \u003cem\u003eS. alterniflora\u003c/em\u003e was more prevalent upslope towards the forest edge (Mendelssohn, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Craft et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1991\u003c/span\u003e; Koretsky et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Negrin et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe decrease in panicle numbers in upper \u003cem\u003eS. alterniflora\u003c/em\u003e zones in both sites, although only significant for site B, may be attributed to the fact that the plots in Site B were closer to the forest edge and may have greater exposure to freshwater discharge, which introduced a greater salinity gradient or more frequent exposure to freshwater sheet flow from the adjacent upland area. Similar to plant height, we found that higher salinity levels were associated with shorter panicle length when the salinity exceeded 18 psu, while panicle length remained relatively consistent by salinity changes below this threshold. The observed changes in plant height, panicle number, and panicle length with increasing salinity indicated that these plants may have specific salinity tolerance thresholds. Beyond these thresholds, plant growth and reproductive features were negatively impacted. The variations in these phenotypic traits in response to salinity stress suggest that plants have developed adaptive strategies to cope with high salinity. These likely involved physiological adaptations such as altering water uptake mechanisms, ion regulation, and osmotic balance to maintain growth and reproduction under saline conditions.\u003c/p\u003e \u003cp\u003eThe relationship between panicle number and length to porewater salinity was particularly indicative of how salinity stress relates to plant reproductive strategies. Fewer and shorter values for these traits under high-salinity conditions could signify a trade-off where plants allocated more resources toward survival rather than reproduction. These patterns reflected the ecological dynamics of marsh ecosystems, where salinity is a key environmental factor influencing plant community structure and function (Pennings \u0026amp; Bertness, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Changes in plant growth and reproductive traits relative to salinity could have cascading effects on ecosystems because of the importance of the structured habitat provided by the stems of marsh vegetation (Lewis \u0026amp; Eby, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Lefcheck et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Future studies should consider plant density across the elevation gradients and zones to consider potential trade-offs exemplified by the self-thinning law in \u003cem\u003eS. alterniflora\u003c/em\u003e (Liu \u0026amp; Pennings, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOur investigation revealed consistent C:N ratio across the elevation and salinity gradients (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), a slight decrease in C:N across in site B and no significant differences in foliar carbon and nitrogen concentrations between the lower and upper marsh for either site (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Although elevated salinity can alter nitrogen assimilation (Bradley \u0026amp; Morris, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1992\u003c/span\u003e), the absence of detectable shifts suggests one or more buffering mechanisms: (1) microbial and sediment processes that stabilize plant-available N across zones; (2) co-limitation by other nutrients (e.g., P or micronutrients) constraining N assimilation independently of salinity; and (3) hydrologic decoupling whereby surface salinity poorly indexes root-zone exposure. To evaluate these mechanisms, we recommend: (1) repeated porewater measurements of electrical conductivity (EC) together with dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) across tidal/rainfall cycles; (2) pairing foliar C:N with N:P to analyze nutrient limitation and N sources; and (3) mixed-effects modeling with site/zone as random effects, reporting effect sizes with 95% CIs and an a priori power analysis to state minimum detectable differences.\u003c/p\u003e \u003cp\u003eOur study highlights the complex interactions between salinity and elevation in shaping growth and reproductive traits of the dominant plant within salt marshes along much of the Atlantic coast of the U.S., \u003cem\u003eS. alterniflora\u003c/em\u003e. The observed variations in plant height, panicle number, and in response to salinity underscore the significance of understanding how these traits are influenced by changing environmental conditions. The adaptive strategies plants employ, including alterations in nutrient uptake and osmotic regulation, are crucial for their survival and reproduction in saltmarsh ecosystems. Given the increasing challenges posed by sea-level rise, as well as shifting storm patterns and associated precipitation, it is essential to further investigate these trait variations and the mechanisms that drive their expression across sites. This knowledge will enhance our understanding of plant adaptability and resilience and inform the management and conservation of coastal ecosystems, where plant community structure and function are tightly linked to environmental stressors.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate:\u003c/strong\u003e \u003cp\u003e No permissions for plant collections were required.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent for publication:\u003c/strong\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThis work was partially funded by Clemson University Faculty SUCCEEDS program and Charles Carter Newman Endowment funds, Clemson University, Clemson, SC. Funding for RPD was provided by the United States NOAA Office for Coastal Management via the annual operating award to the North Inlet-Winyah Bay NERR (NA21NOS420039).\u003c/p\u003e \u003cp\u003eAuthors' contributions: LRO, QS and RK conceptualized the study and methods and planned the execution of data collection. LRO, JAR and RPD conducted the field data collection. LRO and QS synthesized, quality controlled and analysed the data and wrote the results and discussion. All authors contributed to the final writing of the manuscript and approved its final stage.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors would like to thank Shelby Rowland for her contributions to field work and data collection, as well as the NI-WB NERR staff for construction and maintenance of marsh boardwalk infrastructure. This work was partially funded by Clemson University Faculty SUCCEEDS program and Charles Carter Newman Endowment funds, Clemson University, Clemson, SC. Funding for RPD was provided by the United States NOAA Office for Coastal Management via the annual operating award to the North Inlet-Winyah Bay NERR (NA21NOS420039).\u003c/p\u003e\u003ch2\u003eAvailability of data and material:\u003c/h2\u003e \u003cp\u003eThe datasets during and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e \u003cp\u003eCompeting interests: The authors declare that they have no financial nor non-financial competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAnderson, C. M., \u0026amp; Treshow, M. (1980). A review of environmental and genetic factors that affect height in \u003cem\u003eSpartina alterniflora\u003c/em\u003e Loisel. (Salt marsh cord grass). \u003cem\u003eEstuaries\u003c/em\u003e, 3(3), 168\u0026ndash;176. https://doi.org/10.2307/1352066\u003c/li\u003e\n\u003cli\u003eAyres, D. R., Garcia-Rossi, D., Davis, H. G., \u0026amp; Strong, D. R. 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Macronutrient status of tall and short forms of \u003cem\u003eSpartina alterniflora\u003c/em\u003e in a South Carolina salt marsh. \u003cem\u003eMarine Ecology Progress Series\u003c/em\u003e, 55, 63\u0026ndash;72. https://doi.org/10.3354/meps055063\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"wetlands","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wela","sideBox":"Learn more about [Wetlands](https://www.springer.com/journal/13157)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/wela/default.aspx","title":"Wetlands","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Spartina, phenotypic traits, salt marsh, salinity","lastPublishedDoi":"10.21203/rs.3.rs-9214713/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9214713/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHalophytic plants persist in highly saline environments through a range of physiological and morphological adaptations. Even within a single species, trait expression can vary across environmental gradients such as elevation and salinity. However, while variation in plant height has been relatively well documented in species such as \u003cem\u003eSpartina alterniflora\u003c/em\u003e (also known as \u003cem\u003eSporobolus alterniflorus;\u003c/em\u003e smooth cordgrass\u003cem\u003e)\u003c/em\u003e, exploring the extent and patterns of other trait expression across natural environmental gradients provides insight into how multiple environmental drivers shape plant form and function. This study examined trait variability in \u003cem\u003eS. alterniflora\u003c/em\u003e, a dominant salt marsh grass along the Atlantic coast of the United States. Plants were surveyed across an elevation gradient along three transects at two sites within the North Inlet\u0026ndash;Winyah Bay National Estuarine Research Reserve, South Carolina. Here, we document phenotypic traits (plant height, panicle number and length, and foliar nutrients) and identify those traits that vary across elevation and salinity gradients. Plant height declined with elevation (195 cm/m at site A; 180 cm/m at site B) but showed inconsistent relationships with salinity. Panicle number decreased by 1.1 per PSU in some transects, and panicle length declined with elevation (19.8 cm/m at site A; 16.0 cm/m at site B). Foliar carbon and nitrogen showed no significant trends. These findings improve our understanding of how \u003cem\u003eS. alterniflora\u003c/em\u003e phenotypic traits vary relative to marsh elevation and salinity, providing insight into the potential resilience and adaptive capacity of a salt marsh foundation species under changing environmental conditions.\u003c/p\u003e","manuscriptTitle":"Trait variability in a widespread and dominant salt marsh grass in a South Carolina estuary","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-09 11:43:21","doi":"10.21203/rs.3.rs-9214713/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2026-04-03T15:58:05+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-03T15:55:35+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Wetlands","date":"2026-03-27T20:20:08+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-25T06:40:43+00:00","index":"","fulltext":""},{"type":"submitted","content":"Wetlands","date":"2026-03-24T13:04:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"wetlands","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wela","sideBox":"Learn more about [Wetlands](https://www.springer.com/journal/13157)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/wela/default.aspx","title":"Wetlands","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"96efe78b-e330-4cee-8dab-70c468fd2d66","owner":[],"postedDate":"April 9th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-09T11:43:22+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-09 11:43:21","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9214713","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9214713","identity":"rs-9214713","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}