Citation:

Hill, T., A. Oczkowski, E. Santos, N. Moore, C. Kanaskie, R. Martin, C. Wigand, AND E. Davey. Multiple-stressor impacts on Spartina alterniflora and Distichlis spicata. Coastal & Estuarine Research Federation (CERF) 24th Biennial Conference, Providence, RI, November 05 - 09, 2017.

Impact/Purpose:

This study reports results of a multiple-stressor experiment examining the independent and interactive effects of atmospheric CO2, sea level rise (SLR), nitrogen availability, and warming on above- and belowground biomass allocation in two dominant salt marsh species in the northeastern US. The results are of importance to modeling and understanding the fate of salt marshes at multiple scales, from individual stems to whole ecosystems.

Description:

Salt marshes are subject to an array of environmental changes that have the potential to alter community structure and function. Manipulative experiments often study environmental changes in isolation, although changes may interactively affect plant and ecosystem response. We report results of a factorial experiment examining the independent and interactive effects of atmospheric CO2, sea level rise (SLR), nitrogen availability, and warming on above- and belowground biomass allocation in two dominant salt marsh species in the northeastern US: Spartina alterniflora and Distichlis spicata. Growth rates of individual culms were tracked over time, and at the end of the experiment culms were separated into stem and leaf biomass. Computed tomography was used to quantify belowground productivity and characterize allocation to roots and rhizomes. The two species had distinct aboveground responses to environmental change; S. alterniflora allocated more biomass to stem tissue in response to SLR and nitrogen, whereas D. spicata allocation shifted stem-ward only when all stressors combined. However, D. spicata was more plastic in its specific mass, which declined in response to SLR and increased with N and CO2 enrichment. S. alterniflora net aboveground primary production (NAPP) was enhanced by SLR and N, with the response moderated by warming. D. spicata responded more positively to warming and showed evidence of a strong N amplification of the CO2 response. Belowground responses also varied by species. In the presence of SLR, S. alterniflora responded to N, CO2, and warming with increased surficial root and rhizome mass, but no net difference over the profile. D. spicata root and rhizome mass and volume declined with CO2 and combined N-CO2, but differences were moderated by sea level rise and warming. Complex, species-specific responses to environmental change have implications for carbon storage and other ecosystem-scale processes.

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