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Marine Ecology Progress Series

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MEPS 417:73-82 (2010)  -  DOI:

Multiple levels of nitrogen applied to an oligohaline marsh identify a plant community response sequence to eutrophication

Sean A. Graham*, Irving A. Mendelssohn

Department of Oceanography and Coastal Sciences, School of the Coast and Environment, Louisiana State University, Energy, Coast & Environment Building, Baton Rouge, Louisiana 70803, USA

ABSTRACT: We enriched experimental plots in a Sagittaria lancifolia L. dominated oligohaline marsh for 4 yr with one of 4 levels of nitrogen (N) (0, 50, 200, or 1200 kg N ha–1 yr–1) in combination with one of 2 levels of phosphorus (P) (0 or 131 kg P ha–1 yr–1) to investigate nutrient limitation of primary production and plant community- and species-level responses to nutrient enrichment. Overall, significant changes in ecosystem structure and function occurred with N enrichment only; P enrichment had no significant effect alone or in interaction with N. Both 200 and 1200 kg N ha–1 yr–1 stimulated above-ground plant production. Enrichment with 1200 kg N ha–1 yr–1 also increased S. lancifolia tissue N:P ratio, reduced S. lancifolia N and P resorption during senescence, and altered the relative dominance of the 3 dominant species, but had no effect on species richness. We conclude that (1) N limits above-ground primary production in this oligohaline marsh; (2) the plant response to N enrichment is sequential: moderate N loading stimulated plant production only, while high N loading maintained the elevated production and also altered plant tissue nutrients and species dominance, but not species richness; (3) N enrichment beyond the assimilation capacity of the vegetation drives changes in ecosystem structure caused by altered plant nutrient cycling; and (4) linear changes in species dominance with increasing N enrichment suggest that further nutrient enrichment in time or quantity may result in a shift in species dominance and reduced species richness.

KEY WORDS: Marsh · Nutrient enrichment · Nitrogen limitation · Primary production · Relative dominance · Nutrient resorption · Louisiana

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Cite this article as: Graham SA, Mendelssohn IA (2010) Multiple levels of nitrogen applied to an oligohaline marsh identify a plant community response sequence to eutrophication. Mar Ecol Prog Ser 417:73-82.

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