Nitrogen Uptake Varies Regionally in the Salt Marsh Plant Spartina alterniflora

Abstract

Excess anthropogenic nitrogen is a key stressor in coastal and marine ecosystems, where it can alter primary production, create eutrophic and anoxic conditions, and affect biodiversity, structure, and function. The salt marsh cordgrass, Spartina alterniflora, is a foundation plant species in salt marsh ecosystems along the North American Atlantic and Gulf coasts that plays a key role in the fate of this exogenous nitrogen. S. alterniflora exhibits intraspecific variation in plant morphology, plant-microbe interactions, and consumer dynamics, which can drive ecosystem-level responses to stressors. However, little is known about whether or how intraspecific variation may affect nitrogen cycling or plant response to different forms of nitrogen input, even though such variation could have important implications for the marsh response to eutrophication and for restoration efforts. We conducted a greenhouse chamber experiment to test whether plant intraspecific variation or nitrogen form—nitrate (NO3−) vs. ammonium (NH4+)—affect nutrient uptake among six S. alterniflora populations across two geographically distinct salt marsh regions (Plum Island Estuary, MA and North Inlet, SC). All populations demonstrated approximately 0.9 times greater uptake, on average, of NH4+ relative to NO3−. In addition, we documented significant regional variation in absolute NO3− uptake, resulting in an approximately 1.8-fold stronger preference for NH4+ relative to NO3− among SC populations relative to MA populations. Our results indicate that regional intraspecific variation in S. alterniflora and nitrogen form may interact to influence the degree of exogenous nitrogen uptake in salt marshes, potentially influencing our ability to predict marsh nutrient cycling and its impact on marsh persistence.