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Tidal marsh plant species commonly zonate along environmental gradients such as elevation, but it is not always clear to what extent plant distribution is driven by abiotic factors vs. biotic interactions. Yet, the distinction has importance for how plant communities will respond to future change such as higher sea level, particularly given the distinct flooding tolerances and contributions to elevation gain of different species. We used observations from a 33-year experiment to determine co-occurrence patterns for the sedge, Schoenoplectus americanus, and two C4 grasses, Spartina patens and Distichlis spicata, to infer functional group interactions. Then, we conducted a functional group removal experiment to directly assess the interaction between sedge and grasses throughout the range in which they cooccur. The observational record suggested negative interactions between sedge and grasses across sedge- and grass-dominated plots, though the relationship weakened in years with greater flooding stress. The removal experiment revealed mutual release effects, indicating competition was the predominant interaction, and here, too, competition tended to weaken, though nonsignificantly, in more flooded, lower elevation zones. Whereas zonation patterns in undisturbed portions of marsh suggest that the sedge will dominate this marsh as flooding stress increases with sea level rise, we propose that grasses may exhibit a competition release effect and contribute to biomass and elevation gain even in sedge-dominated communities as sea level continues to rise. Even as abiotic stresses drive changes in the relative contributions of sedges and grasses, competition among them moderates fluctuations in total plant biomass production through time.
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This content will become publicly available on March 1, 2026
What’s Going on Down There? Impacts of Long-Term Elevated CO2 and Community Composition on Components of Below-Ground Biomass in a Chesapeake Bay Saltmarsh
Roots and rhizomes play diverse roles in the response of coastal wetland ecosystems to climate change through hydrobiogeomorphic and biogeochemical processes. The accumulation of living and dead belowground biomass contributes significantly to surface elevation gain, redox status through root oxygen loss and exudates, and plant transport of greenhouse gases to the atmosphere. Yet, responses of belowground biomass to global climate stressors are difficult to measure and remain poorly understood. Here, we report on the response of individual components of belowground biomass to 12 years of CO2 enrichment in a temperate tidal marsh. In both a community initially dominated by the C3 species Schoenoplectus americanus and another initially dominated by the C4 species Spartina patens, elevated CO2 increased total belowground biomass and subtly altered depth distributions of some components. In the Spartina community, this effect was the result of the direct effects of CO2 on plant biomass allocation, while any direct response in the Schoenoplectus community was difficult to detect because of changes in the relative abundance of C3 versus C4 species. In the Schoenoplectus community, belowground biomass was positively related to S. americanus stem density. Compared to the C4 community, the Schoenoplectus community had higher root and rhizome biomass and deeper rhizomes. These results highlight the importance of community composition and plant functional traits in understanding ecosystem- and community-scale responses to elevated CO2 and their potential impacts on marsh elevation.
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- Award ID(s):
- 2051343
- PAR ID:
- 10659595
- Publisher / Repository:
- MDPI
- Date Published:
- Journal Name:
- Hydrobiology
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2673-9917
- Page Range / eLocation ID:
- 8
- Subject(s) / Keyword(s):
- Spartina Schoenoplectus Distichlis climate change carbon sequestration sea level rise redox methane
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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