MEPS 354:35-46 (2008)  -  DOI: https://doi.org/10.3354/meps07170

ABSTRACT: We examined the effects of increased nutrient availability on nitrogen (N) dynamics in dominant New England salt marsh plants (tall and stunted Spartina alterniflora and S. patens) using paired large-scale nutrient and ¹⁵NO₃^– tracer additions. This study is one component of a long-term, large-scale, salt marsh nutrient and trophic manipulation study (the Trophic Cascades and Interacting Control Processes in a Detritus-based Aquatic Ecosystem [TIDE] Project). We compared physiological variables of plants in fertilized (~17× ambient N and P in incoming tidal water) and reference marsh systems to quantify NO₃^– uptake and uptake efficiency, allocation of N to tissues, end-of-season N resorption, leaf litter quality and other potential responses to increased nutrient availability. Reference system plants sequestered ~24.5 g NO₃-N ha^–1 d^–1 in aboveground pools during mid-summer, while fertilized plants sequestered ~140 g NO₃-N ha^–1 d^–1. However, NO₃^– uptake efficiency (% of total incoming NO₃-N sequestered aboveground) was higher in the reference system (16.8%) than in the fertilized system (2.6%), suggesting that our fertilization rate (~70 µM NO₃^– in incoming water) approaches or exceeds the uptake saturation point for this vegetation community. Leaf litter quality was clearly affected by N availability; N resorption efficiency was lower in all plants of the fertilized system; senesced leaves from the fertilized creek contained ~43% (tall S. alterniflora), 23% (stunted S. alterniflora) and 15% (S. patens) more N per unit biomass than reference creek leaves.

KEY WORDS: Spartina alterniflora · Spartina patens · Plant ecophysiology · Eutrophication · Nitrogen isotopes · Nitrogen cycling · Marsh ecosystem